THere is a reason you have a snail problem. HAve you been over feeding or do you have plants in the tank that could leave plant matter to collect on the bottom.
I would try to make sure not to over feed and to clean the grvel weekly. Then try and remove as many as you can by hand. You can make snail traps by putting out a piece of zuchini or other veggie and leving it for a while.Eventually the snails will collect on it and all you haveto do is remove the veggie.
If keeping the tank clean and taking them out by hand(it will take a while to get them all) doesn't work you could try some of the smaller loach species.Zebra loaches(botia striata) work, i have them in my tank. Botia robusta and botia rostrata are also peaceful snail eaters but all need to be kept in groups of 3+.
What kind of fish do you have in this tank and what is your cleaning schedual like?How much are you feeding?