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 aims to prevent this problem by either steadily or immediately putting bacteria in place so that when you introduce your first fish, the bacteria are already present and working and there is not a build up of toxins. The big problem with cycling is that there are many different methods, and one fish keeper’s idea of cycling may not be the same as another’s. There are also some rather bad ideas of cycling still floating around, and some impractical ones, so getting it right can be difficult if you don’t get the right advice.
Fish 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 small numbers of fish at a time and stocking gradually and slowly over a period of several weeks or even months. The idea is that, providing feed levels are not too high, the incremental increases in 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 aquariums 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, do a small water change, and if required add some activated carbon to remove the excess. Following the process of adding no more than a few fish each week and testing daily for the first couple of weeks will allow a ‘fish cycle’ to take place. It can take up to a couple of months before your tank can be considered cycled using this method.
Fish cycling with bacterial starters
To help a fish cycle along, and reduce the chances of problems, there are a number of bacterial starter products on the market. These contain live or dormant bacteria that can be added to the tank, and should settle or ‘seed’ the filter. If there is a waste source present, some of the bacteria will settle in the filter medium and start processing wastes. The two most common types of bacterial starter are those containing just the bacteria, and those containing both bacteria and a food source. In a tank with fish already present it is very important to use only the ones without a food source, otherwise the food source (usually an ammonia compound) can have the opposite effect and will raise pollutant levels.
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. There are four methods often described to do a fishless cycle as outlined below
1. Bacterial starters
Using a bacterial starter that contains a food source will seed the filter and provide wastes for the bacteria to live on until fish are added. With this method you add the bacterial starter as recommended by the manufacturer and measure your ammonia and nitrite levels. You should see a rise and fall in ammonia levels followed by a rise and fall in nitrite levels, once both are at zero and continued addition of the bacterial starter does not produce any change from a zero level, you can start adding fish and stop adding the bacterial starter. This is a good method of cycling but it can be a little hit and miss depending on the product you use. Many off the shelf products including some well-known brands are of questionable quality.
2. Adding ammonia
It is possible to add ammonia directly to the aquarium and let bacteria settle and grow naturally, this method is used by some experienced fish keepers and can be the most accurate way to cycle a tank. Unfortunately, the average fish keeper cannot simply buy ammonia and will find accurately monitoring daily dosage rates rather impractical.
3. The food method
Used for many years to cycle an aquarium, many older fish keepers will know of this method of cycling. For a period of time before fish are added, a small amount of food is added to the tank, which then breaks down and produces wastes, causing bacteria to grow in the filter. Quite simply, this is no longer a good method in modern fish keeping – leftover food can create conditions ideal for fungal and bacterial disease pathogens to thrive, and the quantity of waste produced is not easily controlled. Avoid at all costs!
4. Immediate fishless cycling
The most recent, and arguably the best and most likely to grow in popularity is immediate fishless cycling. With this method, bacteria are kept alive in a solution containing a food source, much like a bacterial starter. The difference is that the bacteria can be separated from the food source and placed in the tank or filter. What this means is that rather than adding waste to the tank to feed bacteria, you immediately have a population of working bacteria without the waste product. When you add fish, the bacteria are ready to work on the fishes waste straight away. Getting this process done properly requires a number of things: The bacteria must be alive, they must be in a food solution, they must be separable from the solution, and they must last until fish are added. A product on the market that does this job well is a called ‘bactinettes’, but it is likely that others will follow as the method gains popularity. With an immediate fishless cycle, you can stock much more quickly and can have a reasonable population of fish within a few weeks of filling the tank.
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 cycle’. This argument rather slightly misses the point, however - cycling is often imprecise and it is possible to get just as good results by using a fish cycle as it is from using bacterial starters, and vice-versa, bad results can happen even when you do a fishless cycle. It is always best to try and cycle the tank before adding fish but if there is any element of cruelty in the 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 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 cycle’ whilst water testing and acting on the results is not cruel, but doing a fishless cycle and not testing may be. 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.
Aiding cycling
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, and the same can be done with aquarium gravel. This should always be done just before fish are added to the new tank or the bacteria may start to die from lack of food. If you are setting up a second tank, you can also run the new tanks filter in your established tank for a few weeks to build up a population of bacteria before transferring it across to the new tank when the first fish are added. Regardless of your cycling method, and the claims of some products, aquariums need at least a week to settle before fish can be added.
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