so ive recently heard that my fry tank might benefit from the addition of a few snails. i dont really know crap about snails and never really looked into them before. i also have a 125 tank that i was wondering if snails would benefit in there. which kind are best for my situation with the fry? will snails survive my 125 (there is a common brown Petsmart pleco and a green phantom in there currently)? do they easily over run tanks? are they like duckweed? the herpes of fish tanks, once you get them they are in there for good?