Fishless cycling

From Wikipedia, the free encyclopedia
Jump to: navigation, search

Fishless cycling is a form of "maturing" an aquarium. In this process, ammonia is provided to allow beneficial bacteria to colonize. Fishless cycling can reduce the chance of fish loss resulting from insufficient populations of these bacteria.


The nitrogen cycle in an aquarium

To start the fishless nitrogen cycling process, you need a fish tank, an aquarium filter system, a heater if you plan to get tropical fish, water conditioner, a liquid test kit (test strips are generally slightly less accurate),[1] and a source of ammonia.[2]

Set up the aquarium with all the equipment first. Make sure the filter is running properly. To speed up the process, raise the temperature to approximately 80 °F(27 °C.) Then, add enough ammonia to raise the ammonia concentration to 4~5ppm. Excessive amounts of ammonia will not speed up the cycling process. The source of ammonia can either be from fish food (which will generate ammonia after decaying) or pure ammonia (in the form of either ammonium hydroxide or ammonium chloride). By using pure ammonia, the fishless cycle is faster and more controllable. After a couple of weeks, the first group of bacteria will grow in sufficient quantities to consume the ammonia and convert it to nitrite. In another couple of weeks, a second group of bacteria will be present in sufficient quantities to convert the nitrite into nitrate, which is much less toxic. During the entire fishless cycle process, It is extremely important to have a constant source of ammonia. Monitor both ammonia and nitrite levels in the aquarium on a daily basis. When both are at 0 ppm, carry out a very large water change (70–90%) to keep nitrate in check.[3][4] This will remove most of the nitrate buildup from cycling.

The tank is now completely cycled and can be stocked with fish.


The most significant advantage of fishless cycling is that it can reduce fish loss due to ammonia and nitrite spikes. Fish loss can be very discouraging for beginners of fish keeping, so indirectly, fishless cycling can also help beginners get a good start.

Cycling aquariums using feeder fish is risky because it infects the aquarium with any disease or parasite they happen to have. Fish raised as feeders do not get the same degree of care as non feeders. Fishless cycling avoids this potential problem.

Fishless cycling also allows the aquarium to be partially stocked from the moment it is cycled, if the nitrogen cycle is completed with high concentration of pure ammonia added daily. This makes for faster stocking than having to wait several weeks between each new group of additions to the tank. It can also be extremely useful when the fish keeper plan to stock a tank full of territorial aggressive fish such as African cichlids, where the later added fish can be at a disadvantage.


  • Phosphates are often created as byproducts when decaying fish food is the source of ammonia.
  • There might not be enough ammonia to allow a sufficient population of bacteria to colonize when fish food is the source of ammonia.

Note that these are not problems when ammonium hydroxide or ammonium chloride is used as the source of ammonia.

  • It might cost more than using a few cheap fish to cycle the tank, if you include all the cost of the water test kit, pure ammonia, etc.
  • Pure ammonia cycling is not as quick nor does it allow as higher bio load stocking of the aged filter media method.[5]

See also[edit]