Fish or Fishless Cycling?

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Cycling a fish tank is the process of encouraging bacterial growth which feeds on the waste produced by your fish. This 'maturing' of the filter bacteria can be done with fish in the aquarium or before fish are introduced.

Cycling image over fish


What is cycling?

The processing of waste products from your fish is done by bacteria which reside mainly in your filter. In a new tank there are none of these bacteria, and they will form naturally when wastes are present but there is a tightrope balance of production of wastes and bacterial growth. If we have too much waste and not enough bacterial growth, wastes will build up and the aquarium will start a downward spiral of water quality problems.  Cycling is the process of growing these bacteria, either using ammonia made by fish to provide the food for the bacteria, or by adding ammonia before fish are put in the tank.



Fish-in cycling

The most common method of cycling a tank is also the slowest and arguably most prone to problems, but it is the simplest for new fish keepers who may not be willing to get over complicated from the start. Cycling with fish is basically a process of adding  a small number of fish, waiting till the bacteria grow then stocking gradually and slowly over a period of months. The idea is that, providing feed levels are not too high, the waste produced by small numbers of fish are small enough for bacteria to develop and process wastes before toxic levels rise. Each new addition of fish increases the aquarium's waste load, and the bacterial population grows to accommodate the increase each time. If too many fish are added at once, or the tank is overfed, wastes will increase quicker than the bacteria will grow, and you get toxic conditions. To avoid this, slow stocking and water testing is essential - as soon as ammonia or nitrites start to appear, cut the feeding out,and do water changes to dilute them. New fish can be added once the filter is capable of removing all the waste from the fish currently in the tank. It is a slow process and can take many months.

There are products called bacterial starters which claim to add the bacteria to the tank. Many of these have no effect. They should not be regarded as a short cut.


Fishless cycling

A preferred method amongst many experienced fish keepers is a 'fishless cycle' which aims to get the filter seeded with enough bacteria to cope with fish wastes as soon as they are introduced, thereby heavily reducing the chances of fish being kept in harmful conditions. Some fish keepers will go as far as saying that you must do a fishless cycle, and if you don't you are cruelly exposing fish to harmful conditions. Whilst this is not quite accurate, a fishless cycle done properly is a much safer and better way to cycle a tank. We suggest 2 methods.

1. Adding ammonia

It is possible to add ammonia directly to the aquarium and let bacteria settle and grow naturally. This is the easiest method of cycling as few water changes are involved and enough bacteria are grown in a few weeks to support a full tank of fish without any risk to the fish.

2. The prawn method

If a source of ammonia cannot be located, raw prawns can be used to provide ammonia. The prawns can either be put directly into the tank in a mesh bag, or used in separate container to make ammonia-rich water which can then be added to the tank.

Seeding a cycle

There are many other things you can do to aid the cycling period of a new aquarium. Adding media from an established filter running on a matured tank will immediately put live bacteria in place.This should always be done just before fish are added to the new tank.Up to a third of the media can be safely removed from an established filter. This mature media can be used to seed a fishless cycle, or a small number of fish can be added and the tank stocked slowly over a period of several weeks. Both the donor tank and the new tank, if fish are added, should be monitored for ammonia and nitrite following the media donation.

Is cycling essential?

There is an argument that it is cruel to expose fish to toxic conditions by not cycling an aquarium properly, or by performing a 'fish-in cycle'. It is always best to try and cycle the tank before adding fish but if there is any element of cruelty in the fish-in cycling process, it is from not testing water conditions and not applying immediate remedies should conditions fall outside of ideal ranges. Whatever method of cycling you use, there is always a strong chance of ammonia or nitrite levels going askew, simply because the aquarium is finding its 'balance', so water testing is the overriding element of importance. It is possible to do a 'fish-in cycle' without creating toxic conditions if you are monitoring water quality, so it should not be labelled as cruel on the assumption it puts the fish in a bad environment. It is not possible to avoid toxic conditions if you are not water testing - doing a 'fish-in cycle' whilst water testing and acting on the results is not cruel. It is important that fish keepers and sources of advice learn the difference between the two - you can cycle using any method providing you are monitoring water conditions closely.

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