The filter will not clean up the poop. A Nerite will leave piles everywhere, mostly by the sides of the tank because they like the hard surface of the tank walls. A filter just keeps down the ammonia since snails have such a large bioload. With some extra sponge it should be okay.
I know that nerites pretty much eat constantly. I actually dose ferts in my unplanted tank to try to grow more algae. I'm not sure how fast one would eat an algae wafer but you'll want to stick it to the side of the tank somehow. They do not like gravel and wont probably eat algae off plants because they don't like crawling on the flimsy surface. Also, they are nocturnal so if your snail doesn't seem to be moving once, try checking on him in the morning before the tank lights come on. I always see my snail eating and moving in the morning when the lights are still off and was worried beforehand because I didn't see her moving around much at all when the lights were on.
I got mine from a member here but there is an LFS about an hour away from here that sells them. Keep in mind that they can live in freshwater and saltwater BUT they can only breed in brackish water. They lay eggs but they don't hatch in freshwater (this is good IMO because they won't overpopulated like ramshorns or pond snails). For this reason, you'd need a special set up to breed them which might be why they are not widely available.
I am getting a red cherry shrimp as well for my blind boys tank to clean up fallen food. That was why I initially had an issue with algae. But RCS, unlike nerites, will breed rapidly in freshwater. But they have a smaller bioload and will clean algae on more places than just the tank walls and hard surfaces.
Edit: I'll also mention that the snail also leaves poo stuck to the glass. It REALLY does not bother me but it requires a lot of turkey bastoring (lol). It doesn't take a whole lot of time and I quite enjoy watching my fish while I do it, but it does take quite a bit of maintenance. In a planted tank you don't need to worry about cleaning really well but it still might be an eyesore. ALSO, I'd keep in mind that if you do get a smaller sized snail, it will grow and still have a relatively big bio-load for its size, but cleaning out the poo is easy.
Last edited by AyalaCookiejar; 04-22-2013 at 06:08 PM.