To me it sounds like the combination of warmer temps and lowered oxygen due to decaying plants has pushed the O2 down below the tolerance of the trout.
Note for the future: Excess feed that the trout doesn't eat plus fish waste is adding to the algae problem. 200 trout is quite a few in a 1/2 acre pond if you are trying to keep the water clear. I would personally stick with 50 or even less, and then you will only need to feed 1/4 as much food or less as you do now since there will be more natural forage for them to share.
Think of the fish food as pond fertilizer. It goes in, and if you do not harvest fish, it does not come out. At some point it will be taken up by plants in a form you do not desire.
To combat the nutrients you can plant desirable plants to take up the excess, there are several threads on here about this subject.
Last edited by liquidsquid; 06/30/16 08:42 AM.
