I recently found small clams about the size of a dime a month or so ago in a local river. Since I found them they have been in a 2 gallon tank with a sand substrate. They have been fine and seem to be perfectly healthy. I was told that they would help keep the water clean in my 75 gal. Although I don't really need them to filter my water or anything I'd almost hate to just get rid of them. They would be going in a Malawi tank. They always bury themselves in the sand and only leave they're two small arms out(the one that sucks in water and the one that blows it out). What do you all think? Should I add them? Anybody know of any perks or negatives that could result? Thanks in advance for all your input.