Bill, I almost learned the hard way regarding cold water refuge for trout in summer. By June/30 my pond was completely stratified with surface temps of 72 and bottom at 56. It was my pond's first year with fish stocked in May, no aeration. Visibility was over six feet and no bottom buildup and very little vegitation of any kind. I thought everything was fine, until I noticed there were virtually no fish below the thermocline and most were swimming in the upper three feet apparently gasping. My cold water refuge was useless to these fish as you stated.
I quickly installed aeration and gradually extended run times and diffusor depth and within a week I had uniform temps not exceeding 68 in any depths. After two weeks temps levelled off at 64 top to bottom. I was running aerator only when air temps were lower than water temps. I did not lose any fish and learned that trout will handle warmer water if oxygen levels are maintained.
I did not let my pond stratify this year and everything is fine so far.
