I recently read a post , cant remember where , in it the poster was having unexplained fish loss and a explosion of tiny snails. It was determined that it was likely the huge snail population could have overpowered the cycle of the tank and the tank was having ammonia spikes or some other toxic issues related to the snail infestation. I would attempt to clear out those snails or at least drasticly lower their population till you find out what the cause actually is. It cant hurt anything to curb them in or get rid of them. I dont overfeed and had snails once. I had a terriable time getting rid of them, they came in on a live plant i bought . They got into the tank, gravel, glass, and worst of all the filters, both cannister and hobs. Nasty buggers.