This is one area of the hobby which seems to cause the most problems to new hobbyists. This is partly due to poor information at the point of sale and lack of proper research. It is vitally important that every new aquarium is properly cycled (matured) in order to make it safe for housing fishes. All fish excrete ammonia from their gills and all organic waste eventually breaks down in to ammonia, this means that a new aquarium containing fish will very quickly have a rising level of ammonia. Normally helpful bacteria will make the ammonia safe but in a new aquarium there are no helpful bacteria and so the ammonia will continue to rise unchecked. This has very serious consequences for the fish because ammonia is very toxic to fish.
In order to avoid this problem the tank has to be cycled or matured, this entails growing a large enough culture of helpful bacteria in the filter system to be able to deal with the toxins produced by the fish.
Starting the process
In order to make the process as fast and problem free as possible we have to provide ideal conditions for the helpful bacteria to grow. Their needs are quite simple, they require:
- Clean water with a high oxygen content.
- Warm condition as this will speed up their metabolism and cause them to multiply faster.
- Slightly alkaline water with high carbonate hardness to prevent the pH from falling.
- A source of ammonia.
- You will also need an Ammonia test kit and a nitrite test kit.
Set the aquarium up as though you were going to add some fish and let it run as though fish were present. Turn the lights on during the day and importantly leave the filters running all the time, it is important that the filters are kept running and only turned off for maintenance. On day two turn the thermostat right up until the temperature of the water reaches 30°C which is the ideal temperature for the bacteria to grow, and then add some ammonia (you can purchase a kit which comes with full instructions from most good aquarium shops and this is probably a safer option than using bottled ammonia from the supermarket) as instructed and repeat this over the next few days. After about four days test the water for nitrite and take note of the level. Keep adding the ammonia as instructed until the nitrite level reaches 10 ppm (parts per million) or 10 mg/l which is essentially the same thing. Once this level has been reached stop adding ammonia and simply wait.
What happens next?
Once the nitrite has reached 10 mg/l there is sufficient ammonia and nitrite to grow a large enough colony of bacteria to be able to keep the water in the aquarium safe for all the livestock. The nitrite will be processed and made safe by a second species of bacteria which will already have begun to colonise the filter. With a temperature of 30°C it will take no more than two weeks for the nitrite to fall to 0 which means that the aquarium has been cycled and is almost ready for the livestock.
Before adding any livestock the temperature must be lowered to a suitable level and a 50% partial water change must be carried out in order to lower the nitrate level after cycling the tank. Once the temperature has stabilised at the correct level the first few fish can be added.
Can the helpful bacteria be added to the aquarium from a bottle?
In my view there are still no 100% reliable products out there. Nitrifying bacteria don’t form spores and so can’t be stored very easily.
If I stop adding ammonia when the nitrite level reaches 10 mg/l won’t the bacteria already present begin dying off?
You would think so wouldn’t you, but this isn’t the case. The nitrosomonas which oxidise ammonia toy form nitrite can survive for many months without any ammonia.
Now that the nitrite has all gone and my tank has cycled is that the end of the process?
No, the aquarium will continue to mature over the next six months or so. There is a lot more going on in a biological filter than simply two kinds of bacteria breaking down ammonia and nitrite. There is an whole ecosystem at work with fungi, bacteria, virus, protozoa along with a range of other single celled organisms at work. It takes time for a balance to be achieved and for the filter to begin to work at full efficiency. Being able to process ammonia and nitrite is just the first stage of many.
I have a planted aquarium and when I add ammonia it disappears but no nitrite is produced. What is going on?
Planted tanks need treating differently. Plants prefer to obtain their nitrogen from ammonia so if the tank contains a lot of actively growing plants with the addition of CO2 and a range of fertilisers to maximise their growth then such a tank will be able to house fish without needing to be cycled. But it has to be a ‘proper’ planted tank with actively growing plants for this to work. Simply sticking a couple of bunches of new plants in to the tank and adding fish without cycling it first will lead to disaster.