The Nitrogen Cycle - New Aquarium

By Rick Thibert




If you're new to fishkeeping, the Nitrogen Cycle is the one thing you must understand before you can care for your fish properly.

In a nutshell, the Nitrogen cycle is the process in which toxic Ammonia (NH3) is made safe by a natural process.

Ammonia (NH3), is produced by fish in an aquarium through respiration, urination and deffication. Ammonia may also be produced by uneaten food left to rot in the aquarium, dead fish or similar. This ammonia is what kills most fish in a new aquarium.

Ammonia is consumed by a species of bacteria called Nitrosomonas. This living bacteria is not present in any number in a new aquarium, but take time to establish themselves on your filter media. They are dependent on a flow of ammonia in the water passing over them, in essence feeding them. This flow of water also provides them with the necessary oxygen required to live. What goes in, must come out, so these Nitrosomonas bacteria produce waste of their own, this is called Nitrite (NO2). As the colony begins to multiply you will find that your ammonia readings will begin to drop and your Nitrite (NO2) readings begin to climb. This is desirable and your tank is now beginnging to cycle.

This Nitrite reading is still lethal, but not as lethal as the Ammonia. This Nitirite is then consumed by Nitrobacter bacteria in much the same fashion as the Ammonia was consumed by the Nitrosomonas bacteria, but the end product this time is Nitrate (NO3). Nitrate is again less lethal than Ammonia or Nitrite, but exposure to high levels over time may cause ill-effects to your fish. To best deal with Nitrates, you need to perform water changes to dillute the concentration of Nitrates down. A planted aquarium has the benefit of the plants taking up some of these nitrates for growth. However, as we are mostly cichlid oriented on this site and plants and cichlids don't mix too well because of their inclination to dig and put things where they like them in "their house", plants aren't an option.

A good test kit is essential when cycling a new tank. It is recommended to perform fishless cycling, whereas, you do not put a fish into your tank until your tank has completely cycled. This can be done by placing a couple of prawns or mussels or similar into your tank to rot.

You will know when your tank has completely cycled when you have nil Ammonia or Nitrite and your Nitrate reading exceeds the value of Nitrate of the water you used in the tank to start with. Be aware that tapwater can have varying degrees of Nitrate present in the first instance. It is ideal for you to not allow the Nitrate to rise above the value of the tap water very much before performing a regular water change. Ideally 25% weekly on a cycled tank allows you to maintain a healthy level of Nitrate.