Mine did that too, I have moved it 3 times-- I finally got it happy a little less then middle ways up in the tank with a good moderate flow to it. Maybe try to move it down alittle, if I read your post right you have yours high up in the tank? When mine was there thats when it did this, almost like it was trying to get away from the lights. HTH. Make sure you have a descent flow going to it, alittle more than ripples, that helps remove the "slime coat" that seems to happen with these. That has worked for me. HTH.