Hey Petsmartchic,
Im surprised they arent multiplying, the kind you are referring to are usually called pond snails, and do not require a partner to breed, they lay gelatin like egg sacs in the water on rocks, gravel, filter intakes, plants.. or anything they can! Once you have a few, usually within a couple weeks, your tank is full!! I know I have tons of them in my snail tanks, along with my apple snails and ramshorns! They dont bother me, they eat up some of the waste, and if someone asks me for some, I will send them out to them! Try putting a piece of cucumber or blanched lettuce in the tank to feed them, and im sure they will multiply for you!!
Ang
P.S. I got some of the blue apple snails!! Love them!