Here's what i found: (copied from reefcentral.com)
Cycling the Tank
Unlike a freshwater tank, it takes time for a saltwater tank to be ready for new fish or other creatures. Once the tank has been set up, you’ve added your sand, filled it with saltwater, turned on the heater and started the filters, then you can add the live rock. What the tank needs at this point is bacteria, and it needs to reproduce and spread before your new pets are added. A very easy way to do this is to buy one or two uncooked cocktail shrimp from the deli at the supermarket. Just throw them in the tank and let them rot. As they do, bacteria will grow as a result. Ammonia levels will rise in the tank over the period of a week to 10 days, then it will suddenly drop (observe this with your ammonia test kit), and nitrites will rise quickly over a period of another few days. Finally, the nitrites will drop off completely (reading 0 on the nitrites test), and nitrates will begin to register on your nitrates test kit. As soon as the ammonia and nitrites tests both read 0 on the matching test kits, it is safe to add the new fish.
Cycling the Tank
Unlike a freshwater tank, it takes time for a saltwater tank to be ready for new fish or other creatures. Once the tank has been set up, you’ve added your sand, filled it with saltwater, turned on the heater and started the filters, then you can add the live rock. What the tank needs at this point is bacteria, and it needs to reproduce and spread before your new pets are added. A very easy way to do this is to buy one or two uncooked cocktail shrimp from the deli at the supermarket. Just throw them in the tank and let them rot. As they do, bacteria will grow as a result. Ammonia levels will rise in the tank over the period of a week to 10 days, then it will suddenly drop (observe this with your ammonia test kit), and nitrites will rise quickly over a period of another few days. Finally, the nitrites will drop off completely (reading 0 on the nitrites test), and nitrates will begin to register on your nitrates test kit. As soon as the ammonia and nitrites tests both read 0 on the matching test kits, it is safe to add the new fish.
