I had a plague of snails about 5 months ago. Then they disappeared. I don't really know how much more scavengers would really make a difference because I vacuum the ceramic part twice per week. I did put about 5 small crayfish in the pool. The fish are reproducing like crazy. I was thinking of some kind of predator fish but then they might clean everything out. I'm really learning about the natural balance of things and how everything kind of works itself out. Its tricky messing with nature.