Fish-less cycling

Fish-less cycling is a process which is used to grow nitrosifying and nitrifying bacteria inside the aquarium filter using household ammonia, which is to equivalent  to the ammonia that would normally be produced by fish, other live animals and rotting plant matter inside the aquarium. Without these bacteria, ammonia and nitrite will very quickly rise to levels that are toxic to aquatic animals.

There are actually three methods of cycling which are used most often:

  • Fish-in cycling: the traditional add fish and wait method. Without large daily water changes, the fish will be harmed by ammonia and nitrite, which may cause death, shortened life span and long term health problems for the fish. With the large water changes, it is still a lot of work, often involving testing the water multiple times per day, and takes a very long time. Because the animals are the source of ammonia, stocking also has to be very slow, so it may be as long as 6-12 months before one can stock fully. Even with reduced feeding, there is still the danger that something will go wrong when one is not there to do a water change and leaving the aquarium unattended for more than a day in the first 2-3 months is not an option.
  • Silent cycling: one of the less common and least known methods of cycling. It is very similar to fish-in cycling, with the main difference being that the aquarium is immediately heavily planted, while stocking is still very slow and the feeding is low too. The idea behind this method is that while the bacteria multiply, the plants use up any excess ammonia, so even as the filter cycles, there is never any measurable ammonia or nitrite present. The downside for this method is that it requires experience in keeping the plants well and slow stocking too.
  • Fish-less cycling is becoming more and more popular because there is no possibility of harm coming to animals during the actual process and it allows for higher “starting stock”. This is the method I am planning to use.

First, one needs to decide approximately how much ammonia the fish can be expected to produce. As a general rule, it is assumed that for a half to three quarter stocking, about 4 ppm (or mg/l) of ammonia can be completely processed to nitrate in 12 hours at 24 hour doses, although 2 ppm is enough for partial stocking. I plan to use a 2 ppm dose to start off with, possibly increasing later on, if I decide to add a higher starting stock.

I prefer to use the “dose and wait” method, which involves only topping up ammonia when it actually reaches 0 ppm. The other option is to top up ammonia at 24 hour intervals, but this requires more effort and should not make much difference to the speed of the cycle.

The most common problems I expect to encounter are pH crashes, cycle stalls (possibly due to high nitrites), algae and a slow start to the cycle. The first two, I expect can be prevented or countered by large water changes with dechlorinated and temperature matched water. Algae would result from light and the ammonia in water, the two combined create very favourable conditions for algae growth, so I will not be using the aquarium light for the duration of the cycle. The last is more difficult, but I hope it will not be a problem for me because the best solution for it is seeding the filter from an established filter, while I hope to run this project as if I was unable to get any help with the cycle. Seeding is the addition of a substantial number of bacteria, this is generally achieved by transfer of established media between a filter which has been running in an aquarium with fish for at least a few months and a new filter. Whichever cycle method is chosen, seeding will always speed up the cycle by a few weeks so it is advisable, if the option is available.

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