My girlfriend uses Turtle Clean in her RES tank. For those not in the know, it is aan enzyme that breaks down solid waste so that the biological filter can take care of it rather than having big chunks of turtle poo on the bottom of the tank. I assume it is not safe to use in a FW aquarium with fish, but I really have no idea. Anyone know anything about it? She doesn't and I wouldn't use it as a replacement for water changes. I was just wondering in terms of a supplement for vaccing and to get rid of unsightly fish poo.