Firstly Is this a new tank? Have you recently bought some live plants...you probably bought some live plants. You should know that the plant/s you bought probably had snails/eggs on them and now in reality your going to have snails. THis is quite common. THere are positive and negative effects. Positive...eat algae, eat unwanted food etc... and they provide good food when squashed for fish. Negatives...simply that they multiply like um actually worse than rabbits
oh my really...they multiply??? oh well ive got 3 tanks i can put them in...and bring some back to the pet store i got the plants from.....thanks alot i guess that question was stupid...i just switched over to real plants so im new to the live thing