I'm trying to decide about nerite snails. I've got a 29g with only a tiny bit of algae on the decorations. The amount in there probably isn't enough to sustain a couple snails so, is there something else they eat? In a previous tank I had a couple and liked watching them crawl around, so I want some in this one. I don't want to throw them in and watch them starve due to lack of algae, though.