Nitrogen cycle

The nitrogen cycle is very important for aquarium hobbyists. The whole cycle is the cycle of life for plants and other living beings. The whole thing starts with nitrogen of course, which is in the air and in the food you give to your fish etc. Nitrogen is also part of all organic matter. When living fish produce waste or the food that is given for them is not eaten fully, this all leads to the process of Ammonification. During this process organic matter (dead fish, dead plants, organic waste) is used by bacteria or sometimes fungi to covert organic form of nitrogen into ammonium. Such ammonium when dissolved in water can produce small amounts of ammonia. How much will be produced depends on the water pH. This ammonia is very toxic to fish. This part is very important when you have a freshly setup aquarium, the first stage will be ammonium production, by using test kits you can measure the amount of ammonium and by checking it against the pH level in your aquarium you can find out how much ammonia is in the tank. In established aquarium or after some time in newly setup one, a bacteria will convert the ammonium into nitrite in the process called Nitrification. That kind of bacteria is naturally living in the soil, in the aquarium this biological filter will buildup in your filter medium and in the substrate if enough oxygen and water flow exists there. Nitrite is toxic to your fish and plants. Second type of bacteria will kick in and convert nitrite into nitrate. You really want this bacteria in your filter, those two types of bacteria as well as few others are very important in the aquarium. It takes time to build up this biological filter (2-6 weeks). Nitrate in high dosage can lead to very unpleasant issues, like extensive algae growth (algae blooming) and is not nice for your fish. Nitrate is also consumed by your plants. Check the other blog entry about the Redfield ratio, where I'm explaining how ratio of nitrogen and phosphorus can be controlled to eliminate algae problems. If you have heavily planted aquarium and small amount of fish you may not have a problem with rising amounts of nitrate in your tank, you may even have to rise its level by adding additional one. If your nitrate level is too high, you can get rid of it partially during a periodic partial water change. There are also some chemical treatments which should be only used when the amounts of ammonium or nitrite are really high, try to prevent those things before they happen by testing your water every week or so (during the cycling process before the biological filter works, you should do this even every day or every second day).

Cheers,
Marcin