The Salty Side: Saltwater Aquariums for Beginners

Do You Need To Cycle A Frag Tank?

The main purpose of a frag tank is to house coral frags. When asking, ‘Do you need to cycle a frag tank?’, what you are really asking is what requirements need to be met to ensure coral frags remain healthy, and what do you need to do to make sure you will be able to sell them on? When we consider the fundamental, minimum requirement of coral in any healthy aquarium, we look at lighting, alkalinity, calcium, magnesium, trace minerals and nutrients. These requirements are non-negotiable for successful growth.

frag tank fish

To meet the minimum requirements, we provide the appropriate lighting. We also set up a dosing schedule to keep maintain good husbandry. In fact, it is quite possible to meet coral nutrient requirements by dosing nitrate and dosing phosphate too. However, by simply cycling a frag tank, you are establishing the nitrogen cycle and providing the vehicle for creating nitrate.

What Is The Easiest Way To Cycle A Frag Tank?

When considering establishing the nitrogen cycle in your frag tank there are a number of choices available to you:

  • Use established ‘live rock’

    Live rock is probably the fastest and easiest way of cycling your tank. The rock will be inhabited by nitrifying bacteria that will quickly ensure that any ammonia introduced to your system (detritus, fish waste) will quickly be broken down into nitrate.

  • Introduce nitrifying bacteria

    Nitrifying bacteria can be purchased by the bottle and used to populate dry rock in your tank.

    ATM Colony is widely used for this purpose with great success, but requires fish to be added at the same time.

  • Traditional cycling

    This is the oldest method, but still used.

    This method requires the introduction of ammonia to the system. This can be in the form of a frozen muscle left to rot in the water, or directly dosing ammonia.

    This can take up to 6 weeks to complete.

All of the above methods of cycling requires that your system has the ability to support nitrifying bacteria.

How To Support Nitrifying Bacteria.

In order to support enough bacteria for your system, you will need to provide them with a home.

Home for nitrifying bacteria is live rock, as well as man-made alternatives used for this purpose. See our article on Live Rock for more info.

CerMedia MarinePure 1.5-Inch Sphere Bio-Filter Media for Marine and Freshwater Aquariums, 1-Gallon
  • Ceramic Bio-filter Media with Vast Surface Area AND Open-Flow Porosity
  • Ammonia and Nitrite Removal
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Biological filtration such as MarinePure, are an alternative to live rock capable of sustaining your bacteria responsible for looking after your nitrogen cycle.
A benefit of this filter media is that unlike live rock, which is always organic in shape, these blocks can occupy a relatively small space, but work with the same potential. 

Can I cycle a frag tank using used water?

Unfortunately, using water from your main display will not automatically cycle your frag tank. The bacteria responsible for the nitrogen cycle do not reside in the water column, but as discussed above, in live rock or man-made alternatives. This however, does not stop you using your existing water if you have it available to use. I would only advise against this if you have an existing parasite that could potentially harm your corals, in your display tank.

Can I cycle a frag tank without fish?

It is possible to cycle a frag tank without fish. In fact, cycling should never be done with fish unless using ATM Colony or similar, because of the potentially toxic levels of ammonia and nitrite which exist in the first stages.

As long as you have a source of ammonia present, your tank will begin to cycle.

If you intend to keep a frag tank without fish, you will need to consider dosing an additive like Potassium Nitrate to ensure you always have trace levels of nitrate in your system.

Can I Cycle My Tank Without A Sump?

If you do not have a sump set up for your frag tank, you will still need to provide a harbourage for your nitrifying bacteria.

This may mean that you will need to dedicate part of your tank to some live rock.  Having live rock in your frag tank is not a bad thing.  If you have a few fish they will welcome a somewhere to hide overnight.

Will Live Sand Help My Tank Cycle?

The addition of live sand can help with cycling of your tank in addition to live rock, but not on its own.

Sand it not ideal in a frag tank as it has the potential to trap detritus. It also makes cleaning the tank out harder, whereas a clean glass bottom is easier to maintain.

Wavemakers introduced into a shallow tank will always be beneficial to your coral, but if you have added sand you will find it blowing everywhere.

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