How to Clean a Saltwater Fish Tank (A Step by Step Guide)

How to Clean a Saltwater Fish Tank

Do you have to clean saltwater tanks?  The answer is yes, but the good news is, with the right kind of planning, it does not have to be overwhelming.  Aquarium cleaning is part of maintaining a saltwater fish tank, but with only six steps (half of them you only do every other week), it is easy to have a perfectly clean aquarium. 

You never want to shock your habitat with anything, and that includes over-cleaning.  This step by step guide will teach you how to clean an aquarium(from5 to 500 gallons; the steps are the same).  And, covers everything from cleaning algae from a fish tank effectively to creating an easy to clean aquarium by creating harmony and balance inside it.

The best way to create less work for yourself is to include aquarium cleaner fish and critters that will naturally help you clean and maintain a thriving habitat for your new pets.  However, to keep an algae-free fish tank, you cannot rely on the clean-up crew alone.  We will recommend fish tank cleaning products with helpful videos to carry you through your reefing journey.

A step by step guide to a clean Saltwater Fish Tank

The section will take you through the steps of how to clean a fish tankJust remember the environment you have created in the tank does not like dramatic changes.  Only clean a few elements at a time. 

The basics for cleaning a saltwater aquarium are easy, you have to follow some steps weekly and others every alternative week.

Clean your glass (so you can enjoy watching your fish swim around), test, and remove 10% of your water weekly.  This will support the levels of the important elements within the habitat and help keep the balance in the mini-ecosystem you created.  These topics are covered in steps 1,2 and 4. 

Alternate between cleaning rocks, and other foreign elements in the tank one week.  The following week clean the hidden elements of your system.  We all get busy, but try not to skip too many weeks in your cleaning routine because It is easier to maintain a habitat than to fix problems neglect causes. These topics are covered in steps 3, 5, and 6.

Step #1:  Tests Your Saltwater Aquarium

There are four types of tests that must be conducted, PH and temperature, the major elements, the nutrients, and the minor elements.  In the beginning, conduct these tests weekly to gain an understanding of what is happening to your saltwater aquarium levels and later develop your own schedule to suit your aquarium.

Take a sample of water from the middle of your tank.  Use each of the different test kits to determine the levels inside your tank.  Levels that fall out of range show that adjustments have to be made to the feeding or cleaning schedules or the inhabitants of your tank for a long-term solution. 

For the short-term, if the levels of one element are too low, you will add that element to your tank.  On the other hand, if they are too high there are two options depending on the severity and which element has increased.  For severe surges, increase the amount of water you remove from 10% to 30%.  Alternatively, for less dramatic changes, increase the number of times you drain water from once to twice or even thrice a week until these levels stabilize.

As you become experienced, the amount of testing you conduct will decrease.  Some tests you will have to continue weekly.  Whereas others you will only need to test every couple of weeks once you know the length of time it takes for the levels to change.

Step #2:  Clean your Fish Tank Glass

The best way to clean aquarium glass is to use both a scraper and a magnetic fish tank cleaner. 

Select either an acrylic or glass scraper depending on the material your fish tank is made of.  The rest of the instructions are the same for either.  Use the scraper at a 45-degree angle along the surface.  This action will release debris and other materials into your tank, and you can vacuum later. 

Follow up by using a magnetic fish tank cleaner like the Mag-Float (when released, it floats to the top of the tank making retrieval easier)  to give it an extra polish.  Pull the magnets apart to release it from the glass. 


  • Using a scraper with a long handle will allow you to clean most of your glass without having to place your hand into the water.
  • Keep the magnet cleaner about an inch off the bottom and prevent the pads from getting dusty or the particles will scratch the glass of your tank.
  • Store the magnet cleaner in such a way to prevent dust and other particles from sticking to it and clean it before you use it.

Step #3:  Remove algae from inside your fish tank (Periodically)

Using a toothbrush or other smaller brush clean rocks and edges of the glass to remove algae and other material adhering to the service as well as any overhead pumps and other objects inside the tank.  Do this before siphoning water, as this will release more organic material into the tank.

Step #4: Drain water and remove algae from your sand.

It is time to clean your sand and reduce your water levels. This will keep your tank in balance.

The best practice is to keep a supply of ready to use water in saltwater tanks for the weekly 10% water change.  In addition, keep clean fresh water in a clearly marked container if you must decrease the salinity level of your saltwater aquarium.  Place a heater into the container with the prepared water to heat it to the same temperature as your saltwater tank.

Move onto cleaning your fish tank by vacuuming the gravel (to remove algae and other debris) and drain and replace 10% of the water using an aquarium siphon.  Create suction in the siphon and place the cup into the fish tank and the other end in a bucket, sink, or toilet (not connected to a septic tank). 

Vacuum the sand first, as this will remove some water.  Hold the cup end into the sand with one hand and the pipe with the other.  Pushing the cup into the sand up and down, the more times you repeat this action the more sand will collect in the cup.  Once the debris and other bits have been sucked into the tube, pinch the tube closed, and the sand will fall back into the tank.

Once you have removed 10% water, top up your tank with the same amount from the heated prepared water.  If you have used a bucket discard the dirty fish tank water

There are different fish tank vacuum cleaners or siphons for you to choose from.  In the video below, they use a manual siphon which is inexpensive.  But to create the suction, you will have to either fill the siphon with water by sucking on one end or dipping it in and out of the water until it fills up. 

Some siphons have a pumping ball or similar device that you pump; it will draw the water into the tube to start the suction.  Others connect to your faucet, once you open the faucet the change in pressure will cause suction and drain the fish tank water into your sink.  Be careful, if the switch is turned the wrong way it will drain tap water into your tank.  Others have filters in the head that will prevent sand and small critters from being sucked into the pipe.

Tips if you are using the faucet pump:

  • Siphon water and run the tap slowly to prevent flooding.
  • If you discard water into a bath or sink, clean it with bleach as fish may carry diseases that can infect humans. 
  • You cannot discard the water into your sewer system if it is connected to a septic tank.

Step #5: Clean the hidden parts of your system (periodically)

Clean your skimmer in some of the siphoned water with a toothbrush to remove debris to keep it working efficiently.   Remove pipe lids and covers, scrub salt and algae build-up from the lids, inside pipes, and the areas around them.  This will not only give you a longer life span on this equipment but will prevent these materials from contaminating your tank.

You can use Safe/Easy Aquarium Cleaner which is a chemical cleaner that can be used to clean all the hidden parts of your aquarium.

Step #6: Clean algae off filters (periodically)

Siphon a small amount of aquarium water into a bucket and use this water and a toothbrush to remove debris and other organic material from hard filters and other decorations that may be in the tank.  For sponges and other softer materials, use your hands to gently remove the organic material from them.

These are the six steps you will need to do weekly to keep your aquarium clean and in balance.

The Different Tests for Saltwater Aquariums

This is where things may get a little bit complicated when you do the test changes, but how you do them is easy.  The times you do these tests vary depending on what you are experiencing in your unique habitat.  Although some fish, corals, and the other critters are tolerant of changes, all of them will thrive if you maintain the levels of all these elements.

This is particularly easy; all you have to do is buy and use different testing kits.  I will take you through the various types of testing you will have to perform.  A list of all the different products you will need is at the end of this section.

You need to test your water weekly to keep balance and harmony in your tank.  These factors may vary depending on the fish and creatures you have in your tank.

Also read – Everything You Need to Know About Building and Maintaining a Koi Pond

Summary of the important elements and the ranges that are acceptable for your saltwater aquarium:

  • Saltwater tank temperature:  between 73- and 82-degrees Fahrenheit
  • Salinity for saltwater tank:  between 34-37 (PPT) Parts Per Thousands.
  • PH level for saltwater tank: an alkalinity level between 8-12 DKH
  • Calcium:  the calcium levels need to remain between 350-450 (PPM) or Parts Per Million
  • Magnesium:  between 1250-1350 (PPM)
  • Phosphate:  Maintain phosphate levels under 0.2 (PPM)

These levels will change for any of the following reasons:

  • Feeding your fish and corals
  • Water changes
  • Introducing new elements into your aquarium

There are different tests you need to do in each of the four types of tests listed below (after you have set up your tank and completed the cycling phase).  In the beginning, complete the tests weekly and adjust according to the dynamics of your tank.

Tip: If you add or change any element, you may want to return to weekly testing to understand how the new element alters the environment inside your aquarium.

PH and reef tank temperatures:

Temperature is the permanent test and if you are planning to grow corals, you need to keep a constant eye on the PH level in your tank.  The PH and temperature levels in your tank change throughout the day.  To keep these at a near-constant level, you need to keep PH meters and thermometers in your tank.  This will give you current and accurate readings, and you can change any element if it falls too far out of range.

Temperature monitoring: Aquarium Thermometer

PH monitoring: either the Pinpoint pH Meter or the Neptune Systems APEXEL Controller

The major elements testing

The major elements that you test for are calcium, magnesium, and alkalinity (if you are not using a meter) of your water.  This testing is important to understand the condition of your tank.  If you keep these at constant levels, it will promote the growth of corals and allow the other creatures to thrive.

The levels especially magnesium may change after you drain your water.  Test the levels a few hours after to make sure the levels have returned to the normal range.  If your elements are lower, add these it into your tank until the desired level is achieved.  Add gradually over a few hours.

Hanna Marine Alkalinity or the Saltwater Calcium Pro Test

Hanna Instruments HI736 Phosphorus or the KH/Alkalinity Pro Test Kit

Magnesium Pro

The nutrient testing:

The primary cause of dirty fish tanks are the fish-eating, digesting, and excreting food into the tank creating the nitrogen cycle.  These remains cause changes to the nitrate and phosphate levels of your tank.

The best way to clean algae from fish tanks is to keep it away, and these levels are where you need to concentrate your efforts.  Nitrate and phosphate tests are the two most important ones for your tank.  If you can keep both in balance, algae will not have enough food to grow.

Nitrate is particularly harmful to your tank and the corals and fish that reside in it.  This is the end product of the nitrogen cycle.  The nitrate level in your tank will experience the highest amount of changes within the environment. 

Nitrate feeds the plants in your tank.  Too much nitrate will aid the growth of algae which in turn is harmful to your tank and fish.  Nitrate is harmful to corals, which will turn brown and eventually die, whereas algae will inhibit their growth.  It is important to test for nitrate even if you do not see much algae, and algae don’t grow even if your nitrate levels are high, it needs high levels of phosphate too.

If you are experiencing high nitrate levels, you need to change what you are doing to the tank.

Changing some or all of the following factors on your schedule will make changes to the nitrate level:

  • Less feeding
  • Increase the number of water changes
  • Increase the efficiency of your filtration system like your skimmer (which removes protein from the water)
  • Increase the plant material in your habitat

Phosphate is another plant feeder that will stimulate the growth of algae.  Reefers planning to grow corals need to test for phosphate on a frequent basis, algae attaches itself to the unseen parts of the coral and inhibit their growth. 

With food being high in protein and the fact that these levels cannot be controlled with replacing the water levels in your tank, you need to filter phosphate.  With modern products, it is easier to remove from your tank than nitrate.

Lowering your phosphate levels will reduce the algae in your water regardless of the level of nitrate.  Add a granular ferric oxide to your filtration system, and it will decrease your phosphate levels in your tank.

Salifert Nitrate

Salifert Phosphate Test Kit

The minor element testing

More experienced reefers conduct these tests less often.  If the four main elements of your aquarium are in balance, the testing of these elements are not really important unless you are experiencing a problem in your tank.  However, if you would like to enrich the color of your corals, you need to keep these balances in check.

For beginners, reefers conduct these tests weekly.  Once you understand how your tank will consume nutrients and thereby creating changes to the environment, you may find you will test less frequently.

The four additional elements you may test for are:

  • Copper
  • Strontium
  • Iodine
  • Silicate

There are a variety of testing kits available for you to choose from, depending on your available budget.  There are combination test kits that you can use instead of the ones listed below.

Salifert COPT Copper Test Kit

Salifert Strontium Test Kit

Salifert Iodine Test Kit

Salifert Silicate Test Kit

Or the Red Sea Fish Pharm ARE21515

To remove phosphate Bulk Reef Supply BRS GFO 

How to Prepare Saltwater for Your Aquarium

A lot of people may be put off by keeping a saltwater aquarium because you have to source saltwater.  You can use clean seawater if you have access to it or purchase readymade saltwater from your local pet store.  Most of us select to prepare it at home.  It is cheaper, and you have more control of the water if you make it yourself.

Preparing the water for a saltwater tank is quite easy once you know how.  The best news is because it does not go bad, you can prepare the water in advance when you have more time.  It will be ready when you need it or in an emergency.

Selecting the Type of Freshwater, You Want to Use as a Base for Your Saltwater

You will have different outcomes to the levels in your aquarium, depending on what type of water you decide to use.  The one you select will depend on the amount of money you have and the durability of your aquarium. 

However, the higher quality of the water you select will make an impact on the clarity and cleanliness of your aquarium.  Most hobbyists recommend RODI water as it will make the saltwater aquarium cleaning easier. 

RODI water removes all TDS (total dissolved solids) from the water making the environment friendlier to more sensitive fish and coral.  These fish will thrive in your tank.  Below we list all the different types of water you can use and how to prepare it.  Do not be put off by RODI water, it is the best water for saltwater aquariums and actually the easiest to make.

Ordinary Water From Your Faucet:  

Many hobbyists use this method and have thriving reefs.  Fill a bucket, your filtration container, or a pot with tap water and do one of the following.

  • Leaving it in a container for 24 hours allowing the chlorine to evaporate.
  • Boiling the water to clean it off more unwanted elements.
  • Using the same filtering systems, we use to create drinking water.

Depending on the chemicals your city uses to clean the drinking water and the age of your pipes will depend on the number of elements that will be present in your water.  Your water will be ready for use, test for trace metals and other mineral deposits to indicate what you are adding to your tank. 

Tips if you are using the above methods in combination:

  • If you are boiling the water, there is no point in leaving the water to stand for 24 hours as chlorine will evaporate during the boiling process.
  • If you boil your water and allow it to cool before filtering, you will keep your filtration system cleaner for longer.

Distilled water:

This is the oldest form of water purification that humans invented.  The process involves boiling water to the point of evaporation and allowing it to condensate, and you have cleaner water.  There are two problems with this approach.

The first problem is that many of the bad elements remain behind and will enter your saltwater aquarium.  The other is that this method is the most expensive.  You can purchase this water and it is ready to use.

RODI water

RODI (Reverse Osmosis and Deionized):  This is a process where the total dissolved solids have been removed from the water making it safe to use in your saltwater aquarium.  This process removes all trace elements like copper and other trace metals that may leak into the water supply from the piping as the water passes through it.

This may sound complicated, but there are many diverse machines that can convert ordinary water into RODI water like the Aquatic Life Twist-In 75 GPD.  An inexpensive compact product that can be attached to any faucet or water supply to create RODI water for your fish tank.  Most of them come with fittings for your faucet, but you may have to purchase the correct one from your local hardware store. 

Connect the inlet pipe to your faucet and place the outlet pipe into a large container and turn on the water.  As the water runs through the various filters more deposits will be removed, and the result is RODI water.

If you do not want to purchase the machine, you can purchase RODI water from your local pet store.  This is the most recommended water to use in your aquarium, as none of these metals occur in the reef.  Either way, your water is now ready to use.

Some RODI machines and filtering devices are portable you can use it and pack it away.  Filter, distilled, and RODI water can be purchased in most areas in an emergency.

The type of water you ultimately decide to use depends on your budget and the amount of available space you have to dedicate to the different machines.  They come in many different sizes and prices that will suit any budget and any space you have. 

If the water you use is important, the container you used to store it in is even more so.  Use a food-grade quality container to prevent it from releasing any foreign material into your clean water.  Test the quality of the water before you mix salt into it, you can use a water quality tester.  There are multi-functional testers that will allow you to save on costs.

How to Convert Fresh Water into Saltwater

Fill a container with water either tap, filtered, distilled, or RODI as you have decided to use for your aquarium.  You can use any size container but use a food-grade quality one to prevent any particles from leaching into your water.

Saltwater can be kept for long periods if you keep it sealed. Clean your containers well after use.  This will prevent any external contaminates from entering your reef. 

Tip:  use two different color containers to store prepared freshwater and your saltwater.

Purchase synthetic salt, different brands have different concentrations.  The packaging of the salt you use will give you the amount of salt you need to add per gallon of water.  Sprinkle the synthetic salt across the top in small quantities.

Also read – Best 30 Gallon Saltwater Fish Tanks

Add a small pump like an overhead pump, turn it on allowing it to run for six hours.  This will dissolve and disperse the salt into the water.  After your water is mixed, test the water for the correct salinity, if you need to you can add more salt or water as you require.  Allow the water to pump for another six hours.  You may have to repeat these steps if it is necessary.


  • Keep the container covered while you are pumping the water to keep it free from foreign materials and bacteria that can contaminate the water.
  • Store salt in airtight containers to prevent moisture from getting into it.  The salt will harden into a brick rendering it useless.
  • You need to do two steps before adding this water to your aquarium:
  • Heat the water to the same temperature as your tank
  • Test the water for salinity, PH, calcium, magnesium, and phosphate levels before you use it.
  • If there is a salinity change in your saltwater aquarium, you need to change the salinity of your prepared water.  If the salinity of your aquarium is too high, reduce the amount of salt in your saltwater by adding fresh water.  If the salinity of your aquarium is too low increase the amount of salt in your water by adding salt and mixing it for 6 hours.
  • You cannot add salt directly to your aquarium.

Saltwater aquarium salt Instant Ocean,  this is synthetic salt you add to water to create saltwater. 

BPA Free Plastic bucket is a food-grade bucket safe for all types of storage including your saltwater.

Hydrometer this will check the salinity of your saltwater.

Creating harmony inside your aquarium

An easy way to clean fish tanks is to create a well-balanced environment with the correct mixture of fish.  Some of these fish and creatures will form your clean-up crew, who play an important part in the harmony and help clean up the fish tank.  Some indicate problems within the habitat before your testing will.

Different members of the clean-up crew clean different things and different areas of the tank.  Some will digest the excrement of other fish.  While others will eat the microscopic remains of food and protein left behind.  Many eat plant material, and that includes algae.  Some will consume the dead fish in the tank which would otherwise release harmful trace elements into the environment.

Each member of the clean-up crew will help keep the tank clean naturally.  If you are able to create a harmonious environment in your aquarium, this will make less work for you.  You need to add members with care to ensure that you have enough food for each member to consume.

Even though the clean-up crew is used to help clean the tank, each species has its own interesting characteristics and appearance.  Adding them will create a diverse and interesting environment.  Select ones that match the fish and habitat in your tank which will provide them with enough food and living areas suited for that creature.

No clean tanks are possible to achieve, but if you create balance and harmony within your aquarium you will save on the time and effort you spend cleaning your tank.  To create harmony, you must create a plan and select fish members that are compatible with each other in both temperament and environment.  Select members of your clean-up crew that will consume the waste and are compatible not only with each other but the fish as well.

Understand your primary goal by asking yourself the following questions:

  • What type of reef do you want to create?
  • What are the most important sea creatures or fish you want to keep?
  • What food and how much space each creature or fish will need?
  • Where in the tank will these fish live?
  • How much space and time do you have to dedicate to reef keeping?
  • How much money do you want to spend (there are different options to suit any pocket)?

Once you have answered these questions, you can begin building your tank.  You will add water, coral, and living rocks.  Once your tank has been cycled, you are ready to introduce fish to the tank.  Once the levels of nutrients within the tank are available you will add the clean-up crew.

Many pet stores will advise a number of snails, crabs, and other clean-up creatures for the size of the tank you are planning to build.  This is the end number once you have a thriving tank filled with protein, algae, and other materials to feed them and not at the beginning of your tanks’ life. 

In the beginning, add one or two creatures per 10 gallons of water that can live on the nutrients and the food in the tank and increase once they are thriving.  You will increase their number as you add more fish, and the balance of your tank is reached. 

This will vary depending on the levels your tank forms naturally.  If they look healthy over a period of time and you still have a large algae growth; add one at a time over a period of a few months.  These will not be your primary filtration system.

Some reefers use the clean-up crew as replaceable, but this is not a good option.  As they die, they release harmful chemicals and bacteria into your aquarium, and this philosophy will cause more problems later.  Keep the number small and add more members slowly.

Many salt fish and critters of the same species come from different parts of the sea and live in different temperatures.  Knowing what temperature, you will keep your tank on will help you in your selection of the types of fish and the clean-up crew you can have. 

You need to be careful when making your purchases.  As a rule of thumb, check the temperature of the tank where you plan to purchase them from as a good indicator if you can keep them or not.  Some fish are not compatible with life in captivity and will die.  All deaths in your tanks are harmful to the levels within.

Corals do more than look pretty in your aquarium.  They keep your fish calm and provide a place for them to hide in your tank.  Corals grow by drawing calcium and carbonate from the water creating a structure of calcium carbonate making them grow.

The clean-up crew

Sand filtering fish include the Gobi range including the Blue Cheeked Gobi.  These fish grab mouthfuls of sand, filter it through their gills removing a lot of the edible parts from the sand.  After the fish drop the sand to the floor and sometimes on your corals which will irritate them.  The natural movement of the sand will give your tank a fresh appearance.  They can be kept in pairs or groups with other sand cleaning creatures.

Be careful when you are selecting the type of gobi you want to keep, some species grow to a length of 8 inches.  These need larger tanks, but smaller types are available. Gobis’ live near the bottom of the tank in burrows. 

The Nassarius snail lives under the sand bed and are diverse.  They turn over the sand as they hunt and eat decaying protein before it becomes part of the sand bed.  If you lose a dead fish in your aquarium, this snail will consume it before it can release harmful substances.

The strawberry conch will help clean the tank by moving along the bottom, funneling the sand removing algae, and other eatable material.  In addition, they move along rocks and through grasses cleaning these areas as well.  They are not compatible with hermit crabs.

The Cerith Snail is diverse, they live under the sand and will seldom be seen.  They eat algae leftover food and other material under the soil, keeping that area clean.  The movement of the sand allows oxygen to penetrate the lower levels and allow other noxious gases to escape.  This creates a healthy environment in an area that could otherwise be neglected.  These snails are not compatible with hermit crabs.

Sand sifting Starfish live under the sand bed and feed on detrition and bacteria living within the sand.  This creature will indicate problems in your tank.  If you see it lifting from the sand bed and climbing the glass to escape, this unusual activity indicates something is wrong with your aquarium.

The sand sifting starfish is large, and some grow to be the size of a hand of an adult male.  If you add too many to your tank, you may end up with an imbalance in the nutrient and other levels.  Keep this creature for large aquariums.

Hermit crabs are suitable for small aquariums and most larger ones as well.  Being an omnivore, it is a multi-tasker eating many of the microorganisms you want to remove.  The crab shifts through the sand to eat algae and left-over food.  Their small size hides a large appetite eating throughout the day and with only a few of these creatures can make a dent in the things you need to be cleaned. 

They come in many different sizes and you will be able to find one suited for your saltwater aquarium.  Select the species appropriate for the size of your tank. 

There are two important factors to consider before you decide to keep a hermit crab.  The first is you will have to keep it in a supply of shells as it grows.  They are picky about what shell they choose, and you will need to leave empty shells around your aquarium.  They will try on different ones and decide which one they prefer. 

The second problem is they are not compatible with many snails.  If a hermit crab likes the shell of a snail or if they are in competition for food, they become aggressive and will attack and kill the snails.  Both occupy the same place in the tank, and keeping them apart is unlikely.

You can keep both but you need to be cautious.  Supply enough food for both creatures to eliminate competition.   Scatter enough different types of empty shells around changing them often that the hermit crab will find the one he prefers not making it worth its energy to kill the snail.

Also read – Self Cleaning Fish Tanks That Actually Work

Lists of Different Cleaning Saltwater Fish

There are two key cleaning roles that most reefers are looking for sand cleaning and algae-eating creatures.

Sand Cleaning Saltwater Fish List
  • The Gobi
  • The Nassarius snail
  • Strawberry Conch
  • Cerith Snail
  • Sand sifting starfish
  • Hermit crab
Fish and aquarium creatures that eat algae
  • Crabs
  • Urchins
  • Snails
  • Angelfish
  • Blennies
  • Tangs
  • Sea cucumbers

All of them come in a variety of sizes and colors, and you can select any of them no matter what size or type of tank you have.

Your clean-up crew is closely matched to the type of fish you select to inhabit your aquarium.  I have created a list of the things to remember when choosing fish.

Things to consider when selecting fish:

  • What they eat.  This will include how much food they require; the cost of the food and if it is readily available for you to purchase, or if you can grow your own.
  • The size of the tank they require.  This is dependent on the size of the natural territory of the fish and not the size of the fish itself.
  • How many of the same type of fish you can keep together.
  • The temperament of the fish.
  • The water requirements including PH, Salinity, and temperature.

As a starting point, I have included a list of the top 10 hardest and easiest saltwater fish to keep.

Top 10 easiest saltwater fish to keep

This is a list of the easiest saltwater fish to keep, take into consideration the environment you are creating.  The more harmony you create inside your mini eco-system the easier it will be to take care of.  Balance with no dramatic changes this will shock the environment.  These may be the easiest fish to take care of but consider the temperament, size, and dietary requirements before making a selection.


This is a must for all saltwater fish tank beginners as it indicates problems within the environment.  If the Firefishs’ dorsal fin is erect, this means all is well.  If this fin lays flat on the fishes back, this indicates the fish is in a stressful environment and testing is paramount.


Yes, I know this is not a fish.  An interesting fish tank includes a variety of saltwater creatures.  And this creature made it to the list for two reasons.  They are natural aquarium cleaners extending the time between cleaning giving you more time to enjoy your fish.  The second reason is this creature is hardy, and you have many different options to choose from. 

But like all creatures, they have their problems too.  Susceptible to high nitrate levels, you must remove them from the tank if you are experiencing this problem.  Some fish and animals like the anemone are not compatible with crabs and this will influence the rest of your tank.


This fish is hardy and inexpensive and available in vibrant colors.  However, these fish are aggressive only keep one or two in your tank.


Arguably the best saltwater aquarium fish the second favored fish after the clownfish (a sharp increase of sales after the release of the movie Finding Nemo) hardy and easy to care for.

Mollies live in both fresh and saltwater.  You may have to change it from one to the other.   You cannot make this change sudden, keep the fish in a separate container for a day or two adding a few drops of water from the aquarium every now and again after which you can add the fish to your salt aquarium.


Clownfish are aggressive but hardy and look pretty.  Although, it is best to pair them with an anemone which is harder to look after.  Try to get one bred in captivity as these are easier to keep.


These fish are peaceful and colorful with many different types that will add variety to your saltwater tank.


Hawkfish fall more on the aggressive side but are resilient to changes in the environment. If you are planning to keep invertebrates skip this fish.


With different temperaments, you can select the type of temperament you need for your tank.  Colorful and active they create a pretty picture for your enjoyment.


These fish are hardy and although they are small (only growing to about 3 inches in length) they are aggressive.


These creatures are not only cute to watch and hardy but they are cleaners.  Known for their symbiotic relationship with fish as they keep the tank and fish clean.  Similarly, to the crabs, they are susceptible to high nitrate levels and need to be removed from the saltwater aquarium if these levels increase.

Top 10 hardest saltwater fish to keep

If you are planning to keep a saltwater aquarium, it is more important to know what fish you should avoid rather than what fish is the easiest to keep.  These fish will attract your eye with their uniqueness and color.

The reasons these fish are classified as hard to keep:

  • Their food source is either expensive or difficult to come by
  • The space and habitat requirements they need are going to be difficult to reproduce
  • They are not adapted to live in captivity

Princess anthias:

These fish are beautiful but feeding them is a problem.  This fish is only recommended for experts in the field as it requires tiny plankton type food with a size of 1,5mm throughout the day and needs to be kept in small groups.

Longfin anthias:

This is a deep-water fish and is prone to problems in more shallow waters.  It needs plenty of hiding spaces and you need to keep it in a school of five or more (with only one male).  If that isn’t enough to put you off you need to feed this fish throughout the day.

Blue boxfish:

With a relatively peaceful temperament, its size may vary and even the smallest size fish in this category requires a tank of 180 gallons.  This, believe it or not, is not the problem with keeping this fish.  If these fish experience stress it produces a toxin that will contaminate your tank.

Regal Angelfish:

This fish does not acclimatize to captivity often resulting in death.

Orange spotted filefish

This fish is expensive to maintain.  Either you have to create Small Polyp Stony Corals commonly referred to as SPS coral environment to grow the food for the fish or you have to purchase it from your pet store.

Blue ribbon eel:

This one is much like keeping a snake it needs to hunt for live food.  In addition, it is large and can grow up to four feet in length.  You need to plan your tank with this eel in mind creating plenty of hiding places.  Adding long pipes where it can be completely hidden away as it is timid and needs to hunt.

Harlequin Sweetlips:

This fish requires a large tank over 500 gallons or more and do not thrive in captivity.

Mandarin Dragonet:

Feeding this fish is complicated in the wild they eat copepods, small snails, worms, and fish eggs.  They require an enormous saltwater aquarium for the live rocks (these are rocks taken from the ocean that are filled with a variety of goodies to keep your fish happy) you will have to use them to feed it.  Copepods are available as a living food source.  Check that you are able to purchase these on a regular basis.  

Exquisite butterflyfish:

This fish requires a 155-gallon tank and eats coral in large quantities this makes it one of the most expensive fish to keep.  First, learn how to grow coral and have a good supply before you even think of taking this one on.

Spikefin gobi:

This fish needs to stay in a small tank with minimal hiding spaces.  Only an inch in length it disappears in larger ones.

Also read – What Are the Best 5 Gallon Fish Tanks?

Fish for saltwater fish tank beginners

Selecting a mixture of fish will create an interesting aquarium for you and your visitors to experience.  For beginners, it is better to select fish tolerant to changes until you understand how to create and maintain balance in your aquarium before progressing to other fish. 

To help narrow the choices I have created a table of hardy fish for beginners listing some of the different elements you may want to consider when selecting your fish.

The best way to start is to determine the size tank you can take care of and select your favorite fish suitable for that type of environment.  Select fish that are compatible with that fish and its preferred environment and build up from there.

This table below lists fish according to the most likely position in the tank and the aggressiveness of the personality.  I have included the size and type of food the fish will eat.

15 passive fish and their level in the tank

Name of fishApproximate size in inchesDietNature
Fish that live at the bottom of your aquarium
Blackray Shrimp Goby2CarnivorePassive
Pink Spotted Shrimp Goby5.9 CarnivorePassive
Red Blotched Perchlet2CarnivorePassive
Redbanded Shrimp Goby3CarnivorePassive
Spottail Shrimp Goby6 1/3CarnivorePassive
Fish that will live middle or bottom of your aquarium
Bicolor Blenny5HerbivorePassive
Canary Fang Blenny4 1/3CarnivorePassive
Clown Goby, Citrinis2CarnivorePassive
Clown Goby, Green1 3/4CarnivorePassive
Convict Blenny3 1/3CarnivorePassive
Fish that live in the middle of your aquarium
Canary Wrasse4.7 CarnivorePassive
Chalk Bass3CarnivorePassive
Firefish, Purple3CarnivorePassive
Neon Goby2CarnivorePassive

15 semi-aggressive and aggressive fish and their level in the tank

Name of fishApproximate size in inchesDietNature
Fish that will live at the bottom of your aquarium
Flame Hawkfish4CarnivoreSemi-aggressive
Longnose Hawkfish5CarnivoreSemi-aggressive
Yellow-headed Jawfish3.9 CarnivoreSemi-aggressive
Arc Eye Hawkfish5.5 Carnivoreaggressive
Fish that will live in the middle of your aquarium
Bicolor Dottyback3CarnivoreSemi-aggressive
Blue Devil3OmnivoreSemi-aggressive
Chrysiptera parasema2.8 OmnivoreSemi-aggressive
Coral Beauty Angelfish4OmnivoreSemi-aggressive
Diadem Dottyback2 1/3CarnivoreSemi-aggressive
EightLined Wrasse5 1/3CarnivoreSemi-aggressive
Cherub Angelfish3Omnivoreaggressive
Clark’s Clownfish5 1/2Omnivoreaggressive
Goldbelly Damsel2.8 Omnivoreaggressive
Maroon Clownfish6 1/3Omnivoreaggressive
Pygmy Angelfish3Omnivoreaggressive

Frequently Asked Questions!

How to clean algae from an aquarium?

This will take time to resolve it correctly but drastic changes in the tank will create more problems for your fish and corals, which you want to avoid.  Remember removing algae from the fish tank can take several months and will not happen overnight.

You need to change the environment in your aquarium making it unconducive to algae.  Lower the nitrate and phosphate levels in your tank.  Although this will not remove the existing algae in your tank it will help keep it away once you have removed it. 

To remove the algae from your aquarium you need to take the following steps:

Reducing your feeding (this step is dependent on the number of fish and creatures you are feeding)

  • Create a better filtration system including adding a phosphate filtration kit to your system.
  • Increase the frequency and amount of water changes from 10% to 30%
  • Physically remove the algae weekly.  Pinch the algae into your siphon and vacuum it out of the tank (do not scrub as it releases spores into your tank)
  • Clean surfaces within the tank and then vacuum
  • Adding fish that eat algae to your tank which include the angelfish, blennies or tangs
  • Adding other sea creatures like crabs, urchins and snails will add variety and interest to your tank and will form part of your clean-up crew.  Snails are a good choice as they craw up the aquarium cleaning the algae from the glass.

If the above steps do not remove algae from your tankyou need to use a more aggressive approach.  These may eliminate one problem and at the same time create another.

  • For a more aggressive approach adding good bacteria (Vibrant Liquid Aquarium Cleaner for Saltwater Tanks) to your tank will help remove the algae.  If you are experiencing and algae burst Vibrant Liquid Aquarium Cleaner filled with bacteria may assist if other measures have proven to be ineffective.
  • A fungal treatment that will stop the metabolic process like Reef Flux Anti-Fungal
  • Draining the tank completely and using Dealmed Hydrogen Peroxide directly on the affected areas

Hydrogen peroxide should not damage corals but using a strong chemical may cause other problems and this solution should only be used as a last resort.

Is bacteria beneficial or harmful to your aquarium?

There are both good and bad bacteria in saltwater.  Good bacteria that can be added to solve problems where other less drastic measures were unsuccessful and the bad bacteria which can build up in a tank that is not in harmony will create problems.

Adding bacteria to your aquarium is debated as bacteria will be found naturally in every environment.  A tank in balance, for the most part, will keep both good and bad bacteria in check with little or no assistance from the reefer.  Introducing good bacteria may be useful if you are experiencing a problem within your environment.

There are two basic types of bacteria nitrifying and denitrifying bacteria involved in the nitrogen cycle in your saltwater aquarium.  This is only a fraction of the microorganism within your tank that includes other types of nitrifying and denitrifying bacteria.

Nitrifying bacteria

  • Nitrosomonas Europaea Acuario
  • Nitrosococcus Mobilis Acuario
  • Flavobacterium Oceanosedimentum

Denitrifying bacteria

  • Alcaligenes Denitrificans acuario
  • Paracoccus Denitrificans acuario
  • Rhodospirillum rubrum acuario

Nitrogen is the post-production of fish excrement is the main pollution of your tank, creating an environment for algae to thrive.  Nitrifying bacteria convert nitrogen into nitrate.  This is dangerous to your fish.  Nitrobacteria transforms nitrites into nitrates the food for algae and dangerous to the corals.  Denitrifying bacteria transforms nitrates into free nitrogen and thus ends the nitrogen cycle in your tank.

What is the red slime in my tank?

There are two probable causes of red slime build-up, beginners will find it difficult to identify the difference it is recommended that you treat for red cyano first.  If this fails move on to treat for Dinoflagellates.

Red cyanobacteria slime algae

If you have red slime build-up treat for cyano first as it is the easiest to get rid of and the most probable cause of the red slime.  The red slime will be red with a stringy appearance and lots of bubbles. 

Red cyano breakout will not occur in a well-maintained system.  Create additional flow with powerhead pumps which will help the system overall (you can use these same pumps to mix saltwater).

Have a look at your schedule and the products you use and adjust the simple weekly testing and draining.  Instead of draining only once a week, increase this number to three or four 10% water changes, use RODI water to create your saltwater, clean your rocks and other decorations, and overtime as the aquarium adjust its levels the problem should disappear.

If your nitrate and phosphate levels are high do not attempt drastic changes, complete a 20% – 30% water change over the next few weeks.  If these levels are at 0 you need to increase your feeding and allow the readings to increase as the tank goes through the nitrogen cycle.

After time if the increased maintenance has not achieved the desired results try adding more microflora with either MicroBacter7 or DrTim’s Aquatics If this does not work the cause maybe dinoflagellates.

Red slime caused by Dinoflagellates:

The most noticeable difference is they reduce during the night and reappear in the morning.  You will need to complete all of the following steps.

The first step is adding a UV sterilizer to your system (you may want to add this step anyway as it has other benefits for your tank).  Coralife Turbo Twist UV Sterilizer, 6X,

Increase nitrate by adding nitrate or increasing feeding if your levels are 0, and decrease the efficiency of the filtration system until you reach stable levels.

Increase the micro-organisms in the environment with bacteria as discussed in the section on how to get rid of red cyanobacteria slime algae.

Physically cleaning the sand, stones, glass, and filters every morning.  Over time these steps will remove the red slime.

How to keep a saltwater tank

The most important thing for saltwater fish tank beginners is to remember that Maintaining a saltwater aquarium is far easier than knowing the best way to clean it.  Frequent aquarium testing will ensure your tank is in balance.  If any of the levels within your aquarium change either frequently or drastically you need to look at the basics.  This includes your feeding and cleaning schedule.  Check all your equipment is in working order.

Removing algae and salt build-up frequently will give longer life to the equipment and makes the task of cleaning a saltwater fish tank easier.  As you increase your fish population you will need to increase the saltwater cleaning fish, the clean-up crew is important too.  Check the levels of nitrate during the day and this will give you a good indication of how many clean-up crew members you need to add rather than relying on the number per gallon of water.  Tanks are different.  With proper planning before you make changes will help you create and keep a happy and more importantly a healthy reef.

Also read – Best 20 Gallon Fish Tanks for Beginners

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