Once you've purchased your fish tank, filter, pump, decorations and any other accessories and set up the tank it is time to prepare it for your fish by 'cycling it'. What this means is that you need to provide an environment for the bacteria that will keep your tank free of toxic chemicals to grow. Nitrifying bacteria convert toxic ammonia that is excreted by the fish into, firstly nitrites which are also toxic, and then into the much less toxic nitrates.

There are two ways to do this, one is to introduce some hardy fish into the tank which can survive the higher levels of these toxic chemicals until the bacteria grow enough to deal with them. The second way, which is more humane as it does not involve using fish, is called fishless cycling. In this method a culture of bacteria is introduced and ammonia is used to encourage them to grow.

Ammonia is very toxic to fish and can cause damage to their gills. If you use fish to cycle your tank, even though they do survive, they will be damaged and much weaker. We recommend that you use a fishless cycling method which is very easy to do and only introduce fish in the tank once the levels of toxic chemicals fall to zero.

Fishless Cycling Method

The Bacteria Culture

The first thing you need to do is to obtain a culture of nitrifying bacteria. If you have a friend with a fish tank you can take some of the gravel, filter material or even a piece of rock or decoration from their tank which will be loaded with these bacteria. Failing that bacteria cultures such as Hagen’s Cycle (TM) Cycle or StressZyme can be bought in the pet shop. You can then introduce this culture into your tank.

Sources of Ammonia

Now you will need to introduce some ammonia into the tank. You should obtain household ammonia that is 100% pure and free of any perfumes or other additives. If you cannot find ammonia like this in the local supermarket your local pet shop may sell it. If you know a science teacher or someone who works in a lab this could be another source.

The Tank's Temperature

The temperature of the tank needs to be ideal for growth of the nitrifying bacteria and should be between 85 and 95 Fahrenheit (30 to 35 centigrade). Once the tank is cycled the temperature can be reduced to a level that is more suitable for your fish.

Cycling the Tank

Make sure you have plenty of aeration in your tank and also through your filter as bacteria need oxygen to grow. Add your bacteria culture to the tank and then add a small teaspoon of ammonia to a small tank, one and 1/2 teaspoons to a medium tank and 2 teaspoons to a larger tank. After about an hour test the water for ammonia which should be somewhere between 3 and 5 ppm. If it is lower than this add some more ammonia, leave for another hour, then test again. Once the level is correct you can leave the tank for a few days. Now you will need to test the water for the presence of nitrites which the bacteria have produced from the ammonia.

At this point the ammonia level should drop as it is being converted into nitrites. When the ammonia level drops to zero or is very low add the same amount of ammonia that you added in the first place. Continue to monitor both the ammonia and nitrite levels until they drop to zero. Although it is not necessary you can also monitor the nitrate levels as it is interesting to observe them rising as they are produced from the nitrites.

Once the ammonia and nitrites drop to zero your tank is cycled. Now you should do a 60% water change being careful not to disturb the gravel at the bottom of the tank. Do not change the filter material as this now contains the good bacteria. You should now lower the temperature to a level that is right for the fish you will be going to add. Leave the tank alone for two or three hours then recheck it to make sure ammonia and nitrite levels are still zero.

Congratulations! You have now cycled your tank correctly and can now add your fish. Be careful not to overload the tank with fish immediately. It is far better to add the fish over about a month to allow the bacteria to continue to grow and to be able to cope with the maximum number of fish in the tank.

Maintaining Your Tank

Although we won't go into details of maintaining your tank here we will say that you must be careful to preserve the bacteria cultures that you have carefully encouraged to grow. This means that you should never completely change all of the water, only partial water changes are necessary, and never remove and clean all of the decorations and change the filter material at the same time.