if you are going to put your fish in the tank and cycle it, use your existing rocks without washing them and use live plants they will help you with your cycling more quickly. the used gravel hold good bacteria and the live plants will help with any amonia problems. your fish should tollerate the cycle just fine that way. remember to do between 30 and 50 percent water changes every day or every other day and keep checking the amonia in the tanks daily. you want to try to keep the readings at 0.