OK same page now...I think. First I believe your undersized on your pump. So therefor behind on mechanic filtration. What you are seeing is perhaps an algae build up. Something is out of balance and I believe stepping up to at least 1500 gph with a good filter will get things going in the right direction. About the fish, was this sudden loss of interest at feed time? Have you noticed them foraging around the tank? Have you noticed any missing minnows? Sorry about the confusion off the bat. Welcome