Generally, tanks with snails are cleaner tanks. Mystery Snails do VERY well in established goldfish tanks, and they won't overrun your tank with mini snails. They're attractive with their golden shell, and they look fascinating when they have all their gizmo's and what have you out and working. Although they're long tentacles for feeling their surroundings often get nipped by cichlids or clown loaches. A small snail with a few clown loches will leave you with an empty shell pretty soon, Clowns can't really suck out a big snail, but they will try. PH doesn't really bother them, but somewhere between 7.2 and 7.6 is a good standard. Acidic water tends to rot their shell. Pleco's are still the best at cleaning algae in your tank; however, they're much more expensive.