We have recently looked at the Nitrogen cycle in fish tank aquariums and this is a very important aspect of setting up a new aquarium and should be reviewed before taking any steps with live stock.
To put an idea of time scale on how quickly this cycle takes place, when you first set up a fish tank with new water, filter media and the like it is around 40 days for 1 complete cycle to take place. The graph below shows how this is broken down.
It is now possible to speed this process up and there are tricks of the trade to do this such as adding small amounts of food to the tank each day so it starts to break down and the cycle is started. There are also chemicals that can be added to a new tank to force it to cycle within a much shorter period of time such as the API Quick Start fluid.
As a rule of thumb though you want to be testing your aquarium water once a week to every couple of days to start with as ideal water parameters are that the Ammonia and Nitrite level are zero and Nitrate sits between 20 and 40 and remains stable at these levels. Once you are confident these levels are met then you could start to introduce fish to the aquarium however small quantities at a time and monitor the levels of Ammonia, Nitrite and Nitrate as you are bound to get a bit of a spike in these when you first introduce fish.
The key to fish keeping is patience, especially when first setting up a tank. It is always good to start with hardy fish in a tropical tank which can withstand spikes in these 3 levels and are not easily stressed, the Pearl Danio is a great example of such a starter fish and it was in fact my first tropical fish!