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Cycling Your Tank

Every new nano reef must first go through a process that is referred to as "cycling." This involves the creation and growth of the biological filtration that will keep your system alive. The nitrogen cycle will be the most painful waiting period you will have to endure with your new nano reef, but it is vital that the cycle is allowed to complete.
The process begins with the conversion of solid wastes put into the system by fish, into ammonia. In a cycled system there are bacteria known as nitrifiers that transform the toxic ammonia into less toxic products. The ammonia is transformed into nitrites which are then converted into nitrates. Nitrate removal is done via the weekly partial water changes of 10-20%.

When a new aquarium system is created, these bacterial colonies are not immediately present. They will be introduced into your system when your liverock is added and will grow within the porous rock. The process that triggers the cycle into starting is kind of like a reverse process. There will be denitrifying bacteria present on the rock that you add, but there will be no waste available to feed them. As the bacteria and other life dies off on the rock, ammonia will be created. This new ammonia feeds the remaining bacteria, which will then start the cycle process. Other methods may be used to start the process sooner, such as adding a small piece of uncooked shrimp, that will decay into ammonia.
The amount of time that the cycle is going to take in a new system is difficult to predict. On average, it can take anywhere from two weeks to a month. If the rock is 'uncured', it may take longer for the existing die off to decay. If the rock is 'pre-cured' or 'cured', then the cycle process should complete quicker. More information on these liverock choices can be found here.

So what should you do during the cycle? Keep your lights running on their regular 10-12 hour schedule. Do not cycle your tank with the lights off, unless you want the life on the live rock to die off. Do not perform any partial water changes during the the process, as doing so will stall the cycle from completing. Some people have experimented with doing very small water changes during the cycle to keep the ammonia levels from getting extremely high. The thought behind this method is that it will help preserve the life that came on your live rock. The benefits, if any, are not well known at this time however.

  • MajorReefer, davek17, Eclipse and 35 others like this


Thank you for making this so simple to understand! 

Jul 26 2013 01:14 PM

Thank you for making this so simple to understand! 



I agree! but is there a gallons-time ratio on how long the cycle would take? I have a JBJ 24G and I haven't started, I'm assuming that depending on the amount of live rock and live-sand I decide to put the wait-time would go down. Corrrect? 

Aug 30 2013 12:13 PM

I do not believe there is as the cycle, is the cycle. Now, you can purchase Nutri-Seawater which is "taken from the ocean" and can add livestock same day. There is good and bad to this from what I've read. My JBJ 28G is mini-cycling as I moved tanks. I add Biozyme everyday as well as pH buffer because I had brain farts and used tap water...ok I was lazy and didn't go to the RO unit at our local super market..But I will be using RO or Nutri-Seawater for water changes and then just RO water after I've done a few changes to help with this bacterial growth.

Always wondered, while cycling tank, can I still do top offs w/ fresh water or should this be avoided until cycle is complete?

Yes you have to top up with fresh water. Everyday if you can

I have heard to keep the lights off during a cycling process.  I almost no LR in my DT.  All of it is in the sump.  Should I have a light down there?  

Timeless article.

Jun 08 2014 10:21 AM

Very simple to read and understand. I especially like the diagrams.