We had a few fish dying last week. When we talked to Bob Lusk he questioned whether we were feeding yet. We had just started. He said we may have had some moldy or old food that could kill some of the fish. Check it out and see. I know every year when we start up feeding there is always some dirty food in ours left over from the fall. I would clean it out or stop feeding for a while and see what happens. I have been told by several people that it would be unusual for there to be an oxygen problem this time of year. Not impossible but improbable. Just a thought.