Yeah, those tiny pond snails could take over your tank. When I bought my Mystery snail (which is actually the name of a type of snail), the girl who worked at the store asked what type of snail I wanted and took out one of those little snails. I told her I'd like a nerite snail, which she didn't seem to know what it was.
so she asked what I wanted it for and I said to eat algae, so she was like, "Oh, then you don't want one of these guys. They'll multiply like crazy and take over your tank and even end up clogging your filter."
Then she said, "But some people still like them for frogs and stuff."
LOL so she suggested a mystery snail, which was my second choice after a nerite snail anyway.
My betta attacked it, though, and it died a week later.
Anyway, I'm having trouble with live plants, too. I didn't know Mondo Grass wasn't an aquatic plant (I guess it's a marsh plant so it's not supposed to be fully submerged), so I bought it and it rotted after a couple weeks. I also bought a peacock fern at the same time, which rotted, then I got some type of sword which lasted much longer but rotted too. Then I bought Moneywort, which rotted, and now I have a plant that I don't remember the name of- it was one of the first ones I bought and it's still doing well, and I have some dwarf hair grass. It doesn't seem to be spreading, though.
Anyway, I think my big problem is that I don't have enough light. I'm paranoid about keeping the light on in the tank when I'm not home because I'm afraid the hood will melt and catch on fire or something.
So I really only have the tank light on from the time I get home until I go to bed which sometimes is only about 2 hours. It's near a window, but I don't get very bright light in that side of my apartment. Anyway, light is key. Also, I'm going to start fertilizing.
Sorry that was so long!