Welcome aboard, FPG.

There are two distinct possibilities. I don't know much about aeration, but I believe when you are first starting off with it, you only run it a few hours a day for probably the same issues you mention.

Also, warmer water temps may not allow the trout to survive through the summers.

Do you have a water temp that you can tell us?

You may want to shut the aereator off for now until things settle out.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."