Frag Tank Setup (Complete Guide)

Image Credit: revhtree via Reef2Reef
Image Credit: revhtree via Reef2Reef

Frag Tank Setup (Complete Guide)


If you are interested in your first frag tank setup, this article will provide all the information you need about it. You’ll learn what is the purpose of a frag tank, how to set it up, frag tank maintenance, and how to frag your corals.

What is the purpose of a frag tank?

There are three main reasons why a reefer should consider building a frag tank. First of all, you can use the frag tank to avoid clutter in the display tank. When corals grow too big, you frag them and place them in the frag tank.

The second reason to have a frag tank is to sell corals for money or trade them with your friends without disturbing your main display tank. Selling corals that you grow can be very profitable.

The last reason that makes a frag tank appealing is the idea of a backup. This is valid when you keep the frag tank separate from your display tank (not connected with each other). If something happens to either one of the tanks and your corals die, you don’t start from scratch, you have a backup.

The basics of how to set up a frag tank

Having a frag tank is a great way to expand in the hobby and keep things interesting.

Here are the basics of a frag tank setup:

  1. Reuse or buy a suitable fish tank. 
  2. Decide how you want the tank to be set up
  3. Make a list of accessories that you need to purchase
  4. Set up the frag tank and cycle it
  5. Frag the corals you want to place in the frag tank
  6. Introduce corals and other inhabitants
  7. Monitor parameters and take corrective actions when needed

Selecting a fish tank for your frag tank

The tank you choose for your frag tank can be any size, but there are a few things you need to consider.

The area of it should be large enough for frags, frag racks, or egg crates. For this reason, you should choose a tank that is both long and wide. A 20-gallon tank is more than enough.

Shallow tanks are better because they are easier to clean, easier to access and you’ll have better light penetration. Not to mention it will make adding or removing frags more accessible.

The ideal height of a frag tank is between 12 to 18 inches (30 – 45 cm).

Frag Racks

Frag Plugs


Frag Tank Considerations

Here are some things you need to consider before doing the setup.

Connected to the display tank or not?

You need to decide if you want to make your frag tank connected to your main tank or not. Connecting them side by side can save up costs on accessories and electricity, but you’ll also be at risk of losing all your corals if something happens with either one of them. Pests can easily travel from one tank to another if they share the water.

If you keep your frag tank separated from your display tank, it will be much easier to treat corals if some pests arrive. Even if you have a quarantine tank where you treat your corals before introducing them into your ecosystem, it’s still safer to keep the frag tank separate as well.

It’s cheaper to have both tanks connected and easier to maintain water parameters, but the risks are high. 

Do you need fish in a frag tank?

You don’t need to have fish in your frag tank. Adding them might complicate things since you’ll need to treat water parameters more regularly, however they are great at keeping the algae in check.

Do you need a sump in your frag tank?

While the lack of fish will reduce the organic waste in the water, it is still recommended to have a sump for your frag tank. This will help you keep water parameters stable and reduce the volume of water in the frag tank by placing live rocks and other accessories in the sump.

Do you need a skimmer in your frag tank?

It really depends on the purpose of your frag tag, how big it is going to be, and how often you will feed your corals. Corals eliminate a lot of organic waste that needs to be cleaned in some way or another.

If you don’t have a skimmer, you’ll have to do water changes more often. For a small frag tank which you plan to occasionally occupy with frags, having no skimmer sounds better.

But for a big frag tank with plenty of activity, the water changes might seem too much hassle and therefore indicate having a skimmer as a better option.

So, a nano frag tank can easily work without a skimmer. Once you scale up, that might bring problems.

List of accessories for a frag tank

Here is a list of accessories that you need to have to build a successful frag tank.

Frag tank essentials

  • Filtration: You need to have a filtration system to clean the water up, as corals eliminate organic waste.
  • Heating: You need to heat up your frag tank as you do with your display tank. The typical rule of thumb is 3-5 watts of power per gallon of water.
  • Coral cutting tools: You need to have the proper fragging tools. You can buy a kit as they usually contain everything you need, including a saw, scalpel, and glue.
  • Circulation pump: Water flow is essential for the distribution of nutrients and coral health. You want your frags to grow healthy and pretty, so make sure you have a proper flow pump. Some people use two pumps that are connected.
  • Lighting: If you go with a shallow frag tank, your lighting requirements are not as big as with your display tank. LED lights would be extremely useful as you can easily control their intensity depending on what type of corals you are fragging. T5 lights can also work very well for even distribution across a wide area. The best light for a frag tank is one that is well diffused. 
  • Live rock: Live rocks are essential for frag tanks because they help stabilize the water parameters and provide a medium for bacteria. If you don’t use live rock in your frag tank, you’ll have to clean the water more frequently.
  • Frag racks: They can be of any dimension and style, depending on what you need to put into your frag tank.

Frag Tools

Feeding Tongs

Coral Food

How to cycle a frag tank

Cycling is a term referring to the Nitrogen cycle, a process where beneficial bacteria build up in your tank. You need this bacteria to break down harmful ammonia (NH3) into nitrite (NO2) and then the safer nitrate (NO3).

It is important to cycle a frag tank before putting corals in it, otherwise, ammonia will be harmful to them.

Here are the steps for cycling a frag tank:

  1. Once you have all the required equipment for your frag tank, you can fill it with saltwater and start the nitrogen cycle.
  2. The easiest way to cycle your frag tank is with the help of live rocks. Place the live rock and filtration inside the tank. Let the tank sit with saltwater.
  3. Once your ammonia and nitrite levels are 0 (this can take 4-8 weeks), your tank is cycled and you can add frags to it.
  4. In the first two weeks after introducing your frags, check the water parameters daily to make sure they are stable.
  5. After adding your frags, change the water in the frag tank weekly, at around 20% each time.

How to frag corals

When you frag corals, you’re breaking, cutting, or subdividing a corals colony. It might seem a bad thing to do, but they’re made to flourish in these conditions.

The coral is doing all the hard parts of healing, settling, and growing. You just assist it by starting the fragmentation. You then place your newly coral pieces on flag plugs or live rock. The coral will grow as it normally would if it has the same water and light conditions as in the display tank.

The fragmentation process is natural and it happens to plenty of corals in rough seas during storms. This technique of asexual reproductions allows corals to colonize new places.

Generally, there are two types of corals, hard and soft.

When you cut hard corals it’s pretty straightforward. Use a saw or shredder to cut off the part that you want to place in the frag tank. The size of the frag can be as much as you’d like, also depending on the size of the frag plugs. However, pieces that are smaller than 1 inch might be difficult to attach.

For soft corals, you need more finesse because they are… soft. Scissors usually work the best. The tricky part of fragging soft corals is to know where to cut, as the correct method differs between species. You should check the details of your species of corals to know exactly how to do the coral propagation.

After the frag is placed in the frag tank, you should see some growth within a few weeks if the water parameters, flow, light intensity, and nutrients are similar to the main tank.

How to keep your frag tank free of algae

Algae can become a nuisance for any reef tank if left unchecked. The last thing you want in your frag tank is to have overgrown algae.

Strong water flow

One simple way to keep it in check is to have a bare bottom tank with a strong water flow. The water flow will prevent detritus from settling on surfaces. That’s why sand should be avoided in a frag tank. If detritus settles it will increase the level of phosphates and therefore feed the algae.

Clean-up crew

It is also a good idea to have a clean-up crew in your frag tank. Snails, crabs, shrimp, and urchins are very efficient at eating away the algae from your tank. In the display tank fish can be used for this purpose, however considering the smaller amount of water kept in the frag tank it’s better to use invertebrates.


Frag tanks are a great way to keep your display tank clean and make extra money by selling frags. It is also a backup in case something bad happens to your precious corals.

Even if the initial investment might be costly if you do it the safe way, separately from the display tank, the investment will be soon absorbed by the frags you sold, and then you can enjoy a profit.

If you try to build a cheap frag tank you might have to suffer later in case something bad happens. If you start cheap with a connected frag tank, use the profit to quickly upgrade it and make it separate.

In this way, you can enjoy all the benefits that a frag tank brings to reefers. 

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