Prime isn't going to stop the ammonia from hurting the fish. You are in a fishy cycle, whether you plan on keeping the current fish or not, or whether they are feeders destined to be an Oscar's lunch. High ammonia levels can actually slow down and eventually stop the cycle to the BB you need. Even when doing a fishless cycle, you only dose the tank on purpose to about 3-5 ppm and maintain it in that area while the process happens.
http://www.aquariacentral.com/forums/showthread.php?84598-Freshwater-cycling
Bingo!
The Prime doesn't remove ammonia, it "neutralizes" it...to a point. Also Bob is right on regarding the beneficial bacteria as too much ammonia will hinder their growth.