Agree with bro weileong. The fishes would not add any bacteria to your tank (ok, maybe substantial amounts). Bacteria mostly comes from LR and its cultured on the surfaces of sand, rock, etc. Thats why you see people recommending small sand grades to increase the surface area. Fishes too are a life and its also very cruel to use them to produce ammonia. If you do not like looking at a prawn rotting in your tank, use your urine instead, its works for some people. But all in all, read up more and be patient. Here's a saying for you : "You will never live long enough to make all mistakes and learn from them, so take chances to learn from other's mistakes instead