The basic idea is that a tank that is not 'cycled' will not support any but a small stocking level. 'Cycling' is the establishment of the beneficial bacteria that detoxify fish waste. To accomplish this your tank needs a steady supply of ammonia.
The classic cycling method involves a small quantity of fish (relative to tank size) and a lot of patience. If you put too many fish in, ammonia and nitrite levels will become toxic and fish will die. If you perform a lot of water changes it will be easier on the fish but the cycle can take longer.
I prefer to use fishless cycling. It's cheaper, more ethical, and arguably faster than cycling with fish. Here's a link:
http://malawicichlids.com/mw01017.htm but you can google it and find many others.
What is this bio media that you have set up?