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.

The filter

Filters are essential to modern fish keeping: they are home to bacteria which make the water safe for the fish.

The nitrogen cycle in an aquarium commences at the point where fish and dead plant matter produce ammonia. Some of the ammonia is then used up by plants, but the majority is converted, by bacteria which live in the filter, into nitrite. Nitrite is then converted by filter bacteria into nitrate. Some nitrate is used up by plants and the rest is removed during water changes.

The general format of a filter is some sort of pump which causes water to move through some media. This is usually in the form of an internal filter, an external filter, an air pump powered sponge filter, an undergravel filter, a sump, a trickle filter, a hang-on-the-back filter, and so on. For this aquarium, I will be using an internal filter, potentially moving onto an external later on.

There are three types of media usually used in filter:

Mechanical media:
This media includes various sponges, wool and floss, it physically removes dirt from the aquarium by not letting it pass through the filter.
Chemical media:
The primary function of this media is to adsorb undesirable certain molecules out of the water: for example, activated carbon can be used to remove the remainder of medication after a completed treatment. Some “chemical media” works on the basis of ion exchange. It should usually not be used on an every day basis.
Biological media:
Bio-media is the best media for the bacteria to live on because it is usually very porous, so has a high surface area. It is usually made out of some sort of ceramic material. In an undergravel filter, the bio-media is the gravel and in a sponge filter, it is the sponge.

The bacteria are not particularly picky, so will actually live on any surface they can, regardless of the type of media used.

The first step for setting up the aquarium will be cultivating these filter bacteria. They are present in tap water in very small numbers, so I will be feeding them ammonia to encourage the colony to grow. Once the colony is large enough to support fish life, I will be replacing the ammonia with fish (who naturally produce ammonia).


The filter which came with the kit is a Powerbio 700 by Classica (which is the Arcadia brand for non-lighting equipment). It consists of a standard filter power head with a screw-on spray bar attachment, on top of a filter media housing which contains a cage for loose media (containing carbon) and a rough black sponge (not carbon). The carbon has already been taken out and I will be replacing it with some form of bio-media. I will keep the carbon in case I ever need to remove medication after treatments.