My father in law's pond seems to be having issues. Last night he saw hybrid blue gill gasping for air. This morning there are 4 dead and many still gasping for air. He has his aerators on 24 hours a day for the past 2 days, 4 diffusers in his one acre pond. Prior to this he had the aerators on a time running mostly at night. It is in Worden, IL and has been hot 90 degrees plus.

He hasn't sprayed his pond, doesn't have an abundance of algae, nothing added to the pond this year other than feeding his fish...Which he does by hand.

Any suggestions that I can pass on to him?