A good way to check to see if your rock is populated with bacteria, pull the fish and snails if possible. If not, don't continue with my directions. It sounds like it is considering you have more fish that you plan on moving into the tank with the dry rock. Anyway, pull out everything that is alive and go to the grocery store and get yourself some ammonia. It's like a buck a bottle. Just get the plain old stuff with no coloring or fragrance. Use about 1/4 tsp per 20g of water. Test to make sure you're getting some sort of reading after letting the tank mix around. Once you get a reading of ammonia, 1-2ppm, wait a good 8-12 hours and check again. If the ammonia level hasn't fallen, your rock is not populated. If it has, check your trites. If you have no trites, your rock should be cycled. Add the fish you took out and then slowly add the rest of your fish over the next week or 2 depending on how many and how large they are.
This is basically a fish less cycling method used in freshwater tanks, but I know it works in saltwater as well.
Your tank should already be cycled if you've had the rock with fish in the tank for a good 3 weeks. Another member here named Myteemouse just went through cycling some dead rock that he had. It took him about 2 weeks.
