CLean(vacuum) your gravel well....Do a 50% water change thereafter....Also....Check the filter's media for any clear, jelly like blobs of eggs....You may ask, "how might they look like"....Trust me, you will notice them right away.....Pull, scrape, wipe off, whatever makes you feel comfortable, the egg masses.....ALso....A fun way of ridding snails is purchasing a group of 5 or so Dwarf Puppers....Really cute puffies that are really small, really really small.....Any store should sell these...They go for $2-5 each.....