The Aquarium Nitrogen Cycle

Lets talk Science for a while......To keep fish you need to be able to keep water and to keep water as it should be you need to understand the aquarium nitrogen cycle and how all the different elements of the nitrogen cycle fit together and change the water quality in your aquarium.

The Aquarium Nitrogen Cycle takes place in any body of water and is simply nature's way of dealing with fish waste products.  The potential problems start when man intervenes and starts to mess with the environment and you will not see a better example of a false un-natural environment than an aquarium. 

Most aquariums are trying to imitate a stream or moving water.  In a stream the volume of water per fish is generally much greater than an aquarium so their waste products are easily dealt with by the nitrogen cycle. Aquariums are a confined environment and so you need to monitor things and give the nitrogen cycle a helping hand every now and again.

Three of the parameters which are most important to monitor within the aquarium nitrogen cycle are ammonia / ammonium, nitrite and nitrate. 

These will build up in your  tank simply as a result of putting fish in it. Ammonia and Nitrite are poisonous to fish even at low concentrations.  

When you feed your fish the food will be converted into ammonia either by the fish eating it and excreting waste  or by uneaten food decomposing in the substrate and causing ammonia.  Whatever happens the end product of feeding your fish is Ammonia and without an effective biological filter the Ammonia levels in the tank will quickly increase until the fish become unwell or die.

Fortunately for Aquarium Keepers there are friendly bacteria (called Nitrosomonas) that start to break down and convert Ammonia into nitrite as part of the aquarium nitrogen cycle.  The bad news is that Nitrite is still poisonous to fish so we also rely on the second type of friendly bacteria (called Nitrospira) that then break Nitrites down into Nitrates which are a much friendlier chemical as far as fish are concerned.

Nitrates are nature's fertiliser.  Once the bacteria have done their job the water will contain Nitrates which are removed from the water by plants as part of their natural growth process.  As algae are very simple plants, if you allow the nitrate levels to build up you may well end up with an algae bloom or 'green water'.  Some aquarium plants are better than others at taking nitrate from the water.

The balancing act that you need to master is to make sure that there are enough bacteria in the system to convert the ammonia to nitrites and to convert the nitrites to nitrates.  The nitrate are removed from your tank either through plant growth or through partial water changes.  Whenever you are forced to cut back a fast growing plant, just remember that you are removing nitrates from the tank along with the cuttings!!

Remember......When you first set up your tank there are unlikely to be any good nitrifying bacteria in the water.  It is important to cycle your aquarium to build up the correct balance of these bacteria in both the filter and the substrate to get the nitrogen cycle working effectively. 

Whilst this is going on there will be peaks in Ammonia, Nitrites and Nitrates all of which can be harmful to your fish so make sure at the start that you are checking nitrate levels and doing water changes when needed.

Read about the aquarium cycle next