I have probably 2-3 times the number of snails I started with a year and a half ago in my 75. They breed like crazy for me. You won't really get snails with live rock, maybe the occasional one, but most will die off in transport. Even with as many as I have, they don't give me any problems, just make sure you have screens or guards over your intakes so they can't clog up anything. I actually love to see them all come out at night, plus they help clean my tank.