A FOWLR (Fish Only with Live Rock) tank represents a specialized approach to marine aquaria, focusing on maintaining fish alongside live rocks. Live rocks, contrary to their name, are not living rocks but are home to a variety of marine organisms. These organisms, as highlighted by a study in the Journal of Marine Science, play a vital role in maintaining water quality by significantly reducing levels of ammonia and nitrite, two substances harmful to fish.

In the world of aquarists, the beauty of a FOWLR tank lies in its relative simplicity compared to reef tanks, while still offering a slice of the ocean’s vibrancy and diversity. From selecting the right tank and essential equipment, through the careful process of cycling the tank, to choosing compatible fish and ongoing maintenance, each step in setting up a FOWLR tank paves the way towards creating a healthy and balanced marine environment.

This guide provides an in-depth journey into each of these steps, offering both novices and experienced aquarists valuable insights for setting up a thriving FOWLR tank.

What Is A FOWLR Tank?

FOWLR is actually an acronym. Its full form is fish only with live rocks. It is one of the 3 types of saltwater tanks. And the other 2 are fish only tanks and reef tanks. So you can tell why a FOWLR tank is different from others.

At the core of every FOWLR tank are the live rocks. Contrary to what the name suggests, these rocks are not alive; they are essentially pieces of coral skeleton that have been colonized by various marine organisms. These organisms, including beneficial bacteria, algae, and tiny invertebrates, help to filter the water and maintain a stable environment for the fish.

According to a study in the Journal of Marine Science, live rocks can significantly reduce levels of ammonia and nitrite, two harmful substances for fish.

FOWLR Tank Setup: Step-by-step Guide

Before you even learn about what you can put in a FOWLR tank, you should know what tank size would be ideal for it. Of course, you can choose any tank size that seems convenient to you. However, there are pros and cons for each size.

How to setup a FOWLR tank

While the smaller tanks do not take up a huge space, with so many saltwater elements inside, the environment can easily become toxic if you do not maintain them regularly. On the other hand, larger tanks are not space-savvy, but they are quite safe when mixing several tank elements because they don’t easily cause any harm.

A larger tank tends to be more stable in terms of water parameters, making it easier to maintain a healthy environment for your fish. On the other hand, a smaller tank might be more manageable in terms of cleaning and maintenance. The size of your tank also determines how many and what kind of fish you can keep. For instance, a 30-gallon tank might be suitable for a handful of small, peaceful fish, while a 100-gallon tank could house larger or more aggressive species.

1. Filtration System And Protein Skimmer

The filtration system and protein skimmer are two key components in a FOWLR tank setup. They work together to remove waste products, maintain water quality, and promote a healthy environment for your fish.

Understanding the Filtration System in a FOWLR Tank

A filtration system in a FOWLR tank typically involves three types of filtration: mechanical, chemical, and biological.

  1. Mechanical Filtration: This process physically removes solid particles from the water. These particles may include fish waste, uneaten food, and decaying organic matter. Mechanical filtration usually involves a filter media such as foam, floss, or a sponge that traps these particles.
  2. Chemical Filtration: This process uses various media to remove dissolved substances from the water. For instance, activated carbon is a common chemical filter media that adsorbs various substances, including certain toxins, odors, and discolorations.
  3. Biological Filtration: This process involves beneficial bacteria that break down harmful ammonia and nitrite into less harmful nitrate, as part of the nitrogen cycle. The live rocks in a FOWLR tank provide a large surface area for these bacteria to colonize.

The Role of a Protein Skimmer

A protein skimmer, also known as a foam fractionator, plays a crucial role in maintaining water quality in a FOWLR tank. It works by producing a large amount of fine bubbles in a column of water. Organic compounds, including proteins, fats, and carbohydrates, stick to these bubbles and are collected in a removable cup.

By removing these compounds, a protein skimmer helps to reduce the load on the biological filtration, improve water clarity, and reduce the buildup of nitrate. A study in the journal Marine Pollution Bulletin found that protein skimming could remove up to 85% of certain organic compounds in aquarium water.

Choosing the Right Filtration System and Protein Skimmer

When choosing a filtration system and protein skimmer for your FOWLR tank, consider the size of your tank and the bioload, which is the amount of waste produced by your fish. Larger tanks and tanks with a high bioload require more powerful equipment.

Read reviews and consult with experienced aquarists or aquarium professionals to make an informed decision. Remember, investing in quality equipment upfront can save you a lot of trouble down the line.

2. Water Circulation (Pumps And Wavemakers)

Some might tell you that water circulation is not really an important factor for a FOWLR tank setup. On the other hand, I believe water circulation is something you should prioritize as much as the filtration system.

With enough water circulation, it will help keep algae from taking over the tank. Besides, with enough water flow, it can easily move the wastes away toward the rocks and keep the tank environment cleaner. But how do you ensure accurate water circulation?

Well, for that, you can get water pumps and wavemakers installed. There are many types of them available in the market. You just have to get one that is compatible with your fish tank.

3. Lighting System

If you know how a fish only tank works, you would know that a lighting system is not very important or exactly vital there. The same goes for a FOWLR tank. However, setting up a lighting system can be a basic choice. 

But with the right lighting system in the tank, you can enhance some specific algae growth and help the microorganisms residing in the tank. But what kind of lights work best for a FOWLR tank?

Usually, fluorescent lights are said to be an excellent choice for such tanks. But to many tank owners, they are an expensive choice. The problem with high-powered lights is that you have to install a fan or cooling system to ensure the water temperature and other things remain cool enough.

But as you stock your FOWLR tank over time, many things change in the tank environment. And at some points, the lighting system becomes something you should pay attention to. So you must set it up according to your tank environment to ensure the best for fishes and other microorganisms.

FOWLR tank
FOWLR tank

4. Water Source And Mixing Saltwater

What is your source of water for the FOWLR tank? This is important because tank water is one of the vital things that will either help the fishes and other organisms live or kill them. So you must ensure good-quality saltwater for your tank.

You can either mix saltwater or buy the water from aqua shops. And if you are mixing the saltwater at home, make sure the salt has dissolved properly before pouring the water into the tank. Here is how you can mix saltwater at home:

Pour some water into a bucket and mix salt until the gravity reaches between 1.022 and 1.026. After that, pour the mixed water into the tank. Repeat the process until you have enough water in the tank.

5. Live Rock

The whole thing about having a fish only with live rocks tank is having live rocks in the fish tank. So make sure you have plenty of them, but try not to overcrowd the tank with too many of them. And the best way to know you are adding enough live rocks is to know the quantity.

For each gallon of water in your FOWLR tank, you can add 2 pounds of live rocks. In a reef system tank, the amount is usually a little higher. Because when you have a reef tank set up, you get more nitrogen waste loaded on them.

But it is essential to choose rocks that also look good and can enhance the appearance of the tank set up. Sometimes, when living organisms die, they create a mess on the rocks. So watch out for that too.

6. Substrate

You can add various substrates in your FOWLR tank, such as sand, crushed corals, etc. Usually, the recommended layer thickness for a fish tank is about 1-2 inches. However, that also depends on your tank type, size, and the number of fish you have kept.

For example, if you have a larger tank filled with larger livestock and fish, you can add more substrate and can have thicker layers. And you should also know that the layer does not need to be perfectly flat. But make sure to cover the entire bottom area of the tank so that the glass is no longer visible.

For some FOWLR tank owners, the cost of having sand or similar substrates seems a bit unnecessary. So if you want to reduce the cost, you can just add crushed shells and corals.


7. Tank Cycling

Cycling your tank is a pivotal step in setting up a FOWLR tank. This process sets up the nitrogen cycle, the biological process that detoxifies the harmful chemicals produced by fish waste and decaying organic matter.

The nitrogen cycle begins with ammonia, a byproduct of fish waste and decaying organic matter. Beneficial bacteria, primarily Nitrosomonas species, convert this toxic ammonia into nitrite. Nitrite, while less toxic than ammonia, is still harmful to fish. Another type of bacteria, Nitrobacter, then converts nitrite into nitrate, which is relatively harmless to fish in low concentrations.

This biological process is why live rock is essential in a FOWLR tank. Live rock provides a large surface area for these beneficial bacteria to colonize and thrive.

Step-by-Step Guide to Cycle Your Tank

  1. Prepare the Tank: Install your equipment, arrange the live rock, add the substrate, and fill the tank with saltwater.
  2. Add a Source of Ammonia: This could be a piece of raw shrimp, fish food, or a commercial ammonia source. This will feed the bacteria and kickstart the nitrogen cycle.
  3. Test the Water: Use a test kit to monitor levels of ammonia, nitrite, and nitrate. Initially, you will see a spike in ammonia, followed by a rise in nitrite as the first type of bacteria starts to proliferate. Once the second type of bacteria establishes, nitrite levels will decrease, and nitrate levels will rise.
  4. Wait for the Cycle to Complete: This process can take anywhere from 2 to 8 weeks. It’s complete when both ammonia and nitrite levels drop to zero while nitrate levels are detectable.
  5. Perform a Water Change: A large water change (up to 50%) is recommended to bring nitrate levels down before adding your fish.

Remember, cycling a tank requires patience. Introducing fish too soon can lead to unnecessary stress and health problems.

8. Fish Selection

Choosing the right fish for your FOWLR tank is crucial for maintaining a harmonious environment. Here are some popular choices and their characteristics:

Clownfish3-5 inchesPeacefulOmnivore
Royal GrammaUp to 3 inchesMostly PeacefulCarnivore
Yellow TangUp to 8 inchesSemi-aggressiveHerbivore
Flame AngelfishUp to 4 inchesSemi-aggressiveOmnivore
Green ChromisUp to 3 inchesPeacefulOmnivore

Remember to consider the size, temperament, and diet of each fish. Also, ensure that all fish are compatible with each other and the size of your tank.

How to Introduce Fish to Your FOWLR Tank?

Introducing fish to your tank requires care to ensure a smooth transition for your aquatic pets. Here are some steps to follow:

  1. Acclimate Your Fish: Start by floating the bag in the tank for about 15 minutes to equalize the temperature. Then, slowly add small amounts of tank water to the bag every 10 minutes for about an hour. This process acclimates the fish to the temperature, pH, and other water parameters of your tank.
  2. Introduce Your Fish: Using a net, gently lift each fish from the bag and release it into the tank. Avoid adding the bag water to the tank as it may contain harmful chemicals or diseases.
  3. Monitor Your Fish: For the first few days, keep a close eye on the fish. Look for signs of stress, like rapid breathing or lack of appetite, and monitor the water parameters closely.

Make sure to change your tank water from time to time to ensure a healthy tank environment. Change 5% of the water every week and about 10% every fortnight. It will help you recover the lost minerals.

But do not, under any circumstances, add freshly mixed saltwater to the tank. Also, clean the tank glasses to remove algae and other buildups to help your tank appear more beautiful.

Read Next: Clownfish Tank Setup Guide

Do I Need A Sump For A FOWLR Tank?

The sump is part of the fish tank where all the necessary equipment and accessories are kept. Most aquarists prefer remote sumo as it helps clutter all the visible equipment from the tank and enhances its view. But do you need one when doing a FOWLR tank setup?

Not really. A sump is not mandatory for setting up a FOWLR tank. However, you can add one to keep the distracting equipment tucked away and also to enhance your tank’s water volume. And not only that. Though mild, a sump also helps with the tank’s filtration system and increases stability.

But, as the same thing can be achieved using the filtration system and pumps, most people go by without bothering with adding a sump to their FOWLR tanks.

What Temperature Should My FOWLR Tank Be?

The temperature of the ocean determines what kind of lives it will have. But in captivity, you must know what you will have in your tank and adjust the temperature accordingly. And in the case of a FOWLR tank, the ideal temperature falls somewhere between 75°F-80°F or 24°C-27°C.

But the precise temperature level should depend entirely on the type of fish you added to the tank. So you have to observe your fish and other added organisms to check if they are doing well in the given temperature.

But before you set up a heating system for your FOWLR tank, you must consider several things. Such as-

  • Does your tank have excessive growth of algae and other waste? If yes, setting up a higher temperature might not be a good idea.
  • The tank water must have good water movement and aeration. Otherwise, the water will automatically get warm. And with the increased temperature and additional warmth, the fish can easily suffocate and die.
  • Your environment is also vital for the tank’s temperature rise and fall. So you must pay attention to that as well.

How Much Flow Should A FOWLR Tank Have?

Having an excellent flow rate or turnover is essential for any fish or reef tank. As for the FOWLR tanks, the flow rate should neither be too high nor too low to maintain a healthy tank environment. But what should be the flow rate for such a tank?

For a FOWLR tank, the flow rate should be 10 to 20 times per hour. But the summed-up rate should depend on your tank’s size and its turnover time. Here is how you can find the ideal turnover rate for your FOWLR tank-

Tank size x turnover time = flow rate

It means if you have a 60-gallon tank, you should multiply it by 10 or 20. And the result is the recommended flow rate for your tank, which should be between 6000 gph (gallons per hour) to 12000 gph. However, it is best to stick to the maximum flow rate.

But I also encourage you to check to see if the tank fish seem comfortable enough with the flow rate. You can increase or decrease that depending on their condition.

Does Algae Mean My Tank Is Cycled?

Once you set up your FOWLR tank, minus the fishes, you will notice a gradual change in the tank environment. With all new substrates and organisms added, the tank will smell. And the fresh and clean-looking tank will appear less clean and clear.

The live rocks, and substrates will have green algae growing on them. That is because the bacterial colonies begin to establish themselves in this new environment. And this is entirely natural for both the tank and the wild environment.

And as the algae begin to grow and take over the things in the tank, it means the cycling is nearly complete. It also means the tank is almost ready to have fish and other animals in it.

That’s right! You should never put any fish or animal without letting the newly set up tank finish its full cycle. Otherwise, the fish and animals will not be able to adapt well and may die because of various health and environmental issues.

Can You Have Too Much Live Rock In A Saltwater Aquarium?

One of the main features of a FOWLR tank is its live rocks. But as an aquarist or enthusiast, it is natural to get carried away and fill a big part of the tank with live rocks. Then you wonder if you overdid it. So, can you have “too much” live rock? Or, how much is too much?

Well, there is no specific answer to these questions actually. The amount of live rock you set up depends entirely on your choice and your tank size. But generally, professional aquarists suggest adding around 1 pound of live rock for each 1.5-2 gallons of water.

So you can tell that it is natural to add a good amount of live rocks to the tank. But you should also know that live rock can easily trap wastes, making it necessary to maintain the tank more often if you have a lot of them. That is why it is best to keep them slightly far from the tank glass so that you can clean them easily.

On the other hand, the live rocks should not block or limit your tank’s water flow, pump, filtration and swimming of the fish. If that happens, it is likely that you have set up too much live rocks.

Do Saltwater Fish Like High Flow?

There is always debate and confusion regarding whether or not saltwater fish like high water flow. And before knowing the answer, think of it this way-

The ocean is vast and wild. And there is no way for the flow to adjust, which goes on its own way. So saltwater fish are quite used to living and breeding in a high-flow environment. However, things in captivity can be different, and the flow rate depends on the tank’s size and what you have in it.

Nevertheless, it is better to have a high waterflow for saltwater tanks. Many people start with a low flow rate and increase it later. But that can be an issue with the fish’s adaptation skills. You can add multiple flow pumps and check if the fish are swimming around happily. If nothing seems out of place, your tank has the right flow.


Setting up a fish tank is not an easy job, especially when you are new to this. But most beginners prefer learning about a FOWLR tank setup because it helps you learn to set up other tanks comparatively effortlessly.

In a FOWLR tank, you not only keep fish but also live rocks. So you have to set up an environment that is suitable for all the inhabitants. And I believe this guide will help you achieve that easily.

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