Cycling a New Marine Aquarium
The Nitrogen Cycle is Essential to the Health of Your New Fish
Feb 29, 2008
Imagine for a moment that you are given a sterile glass box. Now fill that glass box with saltwater. It’s pretty isn’t it? The water virtually sparkles because it is so clean and clear and crisp. Now imagine heading down to the local fish store and buying a True Percula Clownfish (Amphriprion percula) and putting it in your glass box. At first the clownfish seems quite happy, but then, it starts not to look so good. What’s happening?
A Sterile Marine Aquarium is Not a Good Aquarium
The truth of the matter is that your clownfish is poisoning itself with its own waste. A sterile marine tank is, in fact, the worst kind of tank. In a mature (or “cycled”) tank, beneficial bacteria break down fish waste before it reaches toxic levels. While you still need to perform regular maintenance and use a reliable filtration system, the fully cycled tank is a much more stable environment.
It’s all about the Nitrogen Cycle
The phrase “cycling a tank” refers to the nitrogen cycle where fish waste (ammonia) is converted by bacteria to nitrite (NO2) and then the nitrite is converted by other bacteria to nitrate (NO3). Nitrate, unlike nitrite, is much, much less toxic than ammonia and, providing you do regular water changes, nitrate will not build up to levels toxic to your fish.
The Best Way to Cycle a New Tank
The best way to cycle a new tank is to add live rock. Live rock is not actually alive, of course, but it comes from the ocean (either aquacultured or from reef rubble zones) and is full of life. During the process of getting the live rock from the ocean to your aquarium, a certain amount of life on and in the rock will die. When you add this live rock to your new aquarium, it will prompt the nitrogen cycle as the dead and dying organic matter begins to decompose providing ammonia for beneficial bacteria.
Over the course of the next two to four weeks, the rock will “cure” and the tank will cycle. During this time, it is important to run a filter on the tank and insure that strong flow keeps detritus from settling. Frequent water changes will also be necessary. Be warned, this can be a smelly process. For this reason, some people choose to cure their rock in a separate container in the garage (a trash can with several powerheads and a heater will suffice). If you do cure the rock elsewhere, you will still need to still cycle the tank when you add the live rock after it has cured.
How Do You Know the Tank Has Cycled?
The only way to know whether or not your marine aquarium has cycled is to monitor the water quality. A simple test kit available at aquarium stores will allow you to test for ammonia, nitrite and nitrate. By testing daily, you will notice an initial spike in ammonia over the first week followed by a spike in nitrite toward the end of the second week. When you have recorded these spikes in ammonia and nitrite, you need to wait until both fall to zero. When they do, your tank is cycled, and you are ready to start adding livestock.
Some Final Thoughts
- Adding livestock to your tank may prompt another mini-cycle, which is why you should only add a few fish at a time and wait for ammonia and nitrite to fall to zero again before adding more fish.
- If you do not see the initial ammonia and nitrite spike, you may need to give the process a little nudge. Try adding a raw table shrimp in a net bag (pantyhose work great). The decomposing shrimp should get the cycle started.
- Although so people will tell you to cycle your tank by adding a hardy fish such as a damsel, don’t do it. While the fish may survive, such a practice is archaic and is really nothing short of torture.
- Each tank is different, and cycling times may vary depending upon the quality of the live rock and many other factors. Make sure you to monitor the water quality—that is the only way to truly know if your tank has cycled.
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