If you're gonna get mystery snails, make sure you get Pomacea Brigesii and not Pomacea Canaliculata, they will destroy all your plants.
I bought four Canas and had to buy a new 10G tank for them, but it looks like I might have to get a larger tank. They're getting big really quickly and have a huge bioload, they're messier than any fancy goldfish I've ever seen. I'm gravel vac'ing once every other day.