I gave my brother a histrix ray to put in his tank with discus and 4 ping pong sized apple snails. After about a month of this combo he noticed a small circular piece of skin missing on the rays back. Maybe the size of a pin head. I figured maybe he bumped it on something since he likes to swim a lot. Well my brother called me tonight and said it's back looks better but now the same size spot is around the rays eye. I told him I bet it is those snails but not sure. Does anyone have any ideas? Those snails are fast and will eat meat. I am thinking at night they are crawling on the rays back. The discus are only 3 inch so I know it is not them.