They definitely sound like common pond snails. A picture of them (though not mine but definitely the same type of snail) is:
Hmm, I really thoguht they were laying eggs above the water. I see them every now and again going to the water line and I also see some wee dots appearing. I haven't been removing them because I thought they were eggs, apparently it's just wee tiny bits of leftover flake food or something. I'll have to clean them off now. I feel quite bad, and silly, for leaving this, whether it's food or dirt or what. Ahh well, at least I know noe
I also have one of these snails that also hitchiked on a plant:
Again this isn't my snail but it's definitely the same type. I only have one of these. Can it breed on it's own or does it need another? I think it might be a trumpet snail but I'm really clueless when it coems to snails so I don't know.
Thanks for your help.