Maturing a Tropical or Coldwater Aquarium

Once you have had your aquarium up and running for 24 hours or so, it should be up to temperature and you will have had chance to identify any teething problems with the equipment. Although it appears that the aquarium may now be stocked with fish, there is still a long way to go before it is fully mature. This is because the fish rely on a population of good bacteria in the filter and on the surfaces in the aquarium to consume their waste. It takes around a month to get the bacteria established in sufficient numbers – this process is known as ‘cycling’ the aquarium.

Starting the cycle: until some organic waste is added to the aquarium, the population of good bacteria needed for the filtration cannot start to develop as they need the waste for food. This means that there’s no great benefit to leaving the tank running without adding anything – nothing will happen. The process of establishing the filter bacteria is known as ‘cycling the tank’.

Cycling the aquarium with fish: the more old-fashioned way to cycle an aquarium is to add a small number of hardy fish. The fish waste builds up in the water and then declines as the bacteria multiply. After a few weeks the filter has a good enough population of bacteria and the fish waste levels have zeroed out. At this stage some more fish can be put in – but not before checking the level of fish waste! Ammonia and nitrite are the nasties that need to be at zero before more fish can be added – we can test the levels for you if you bring in a sample of the aquarium water or alternatively we also sell the test kits, should you wish to check the water quality at home. The water quality during cycling and the speed of cycling can be vastly improved by adding a dose of good bacteria (various brands are available – see us in store for the options) – this is best done on the day that the fish are first added. There are some disadvantages to cycling with fish – the first fish in have to endure raised levels of waste. The fish should be able to cope providing suitable species are chosen, a low stock level kept to and the fish fed very carefully. Careful feeding means a very small amount for the first month or so – for small fish such as tetras one flake of food for each fish and once every two days would be a sensible feeding strategy. It’s important not to add more fish after the initial stocks have been added – the ammonia level will soon rise and newcomers find it a shock when transferred from a mature shop tank to a new one where the cycle has not completed.

Fishless cycling is becoming more popular as it avoids exposing your first fishes to the waste build up. To do this a dose of simulated fish waste is added to the tank, to give the filter bacteria something to feed on. A product such as Waterlife ‘Biomature’ is an example of a good agent to start a fishless cycle. The fishless cycle can be left to run in the same way as using fish to cycle an aquarium, in which case it will take around a month to complete, or a dose of good bacteria can be added to speed things along. Cycling in this way means that you can’t add any fish for the first month or so, but does mean that when selecting your first fish there is more choice as you are not restricted solely to hardy types.

If adding live plants to a new aquarium it’s best to do this on the same day as the first fish. If the plants are added first and then the fish added later, even by a few days, in some cases the plants have created some pollution, which has started the cycle and shock the fish when they are added.

When stocking fish in a tropical or coldwater tank, it’s always best to add them in small batches to allow time for the filter bacteria population to adjust. This applies not only to newer set-ups but also established aquaria that have only a few fish left.