I have a 10 gal thank with a fire shrimp cardinal and little clown fish. It's been up for around 2 years and I do weekly 1 gal water changes with RO and keep my ca, alk and ph balanced. I check amonia, nitrite and nitrate periodically with no change. It's in a book case so the filtration is very basic with one power filter and power head no skimmer. I'm not sure why I can't keep snail alive when the other animals do fine. Is there something I'm missing?