I have tried to add Blackhorn snails twice but they never took. I also added 5 gals of clams but they never took for some reason either. However I do have lots of the small pond snails that do show up on their own and they do their small part eating algae. I'm just guessing but it would seem to me that if you are far enough south in east Texas that Tilapia would survive year round. I was stationed in southern Oklahoma and we had snow there.