How many fish and what types do you have?
My personal rule is 1 snail for every 2 gallons. With the right combo of snails, this has worked for me.
For example:
I have a 180 with 2 tangs, a clown, 2 pj cardinals, 1 yellow cirrus wrasse, 1 melanarus wrasse, 2 red striped gobies, 1 sand sifting goby, 1 black com tooth blennie, 3 fairy wrasses, 1 coral beauty
I have for a cleaning crew: 1 fire shrimp, 1 skunk cleaner, 40 trochus snails, 15 Astraeas, 25 nerites, 15-25 nassarius
I have a few random limpets, albalones, a miscellaneous snails, but the majority are listed above.
I did have cerith snails and a few bumble bee snails, but anything small my yellow cirrus wrasse kills :-/
I hate my nerites, they lay eggs all over the place, but they're good glass cleaners. If I had it to do all over again, I'd probably pack my tank with nassarius and trochus and maybe a few Astreas.
I hate Turbo snails - they knock too many corals over