In our pond I thought the same thing deep = cold. We are at 16 feet on one end and 14 feet on the other end. Both ends have bottom defusers set at about 18"s off the bottom. The whole pond warmed to 70 having them run 24/7 in the summer. I would have never believed this unless I seen it that two vertex disks could move one acre of water that deep to warm it all that deep too.

I just have perch and no trout but to help cool the pond I run my waterfall at night and not during the day when the water temp rises.

Cheers Don.

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7/8th of an acre, Perch only pond, Ontario, Canada.