With your diffuser set in 9 feet, there's a good possibility that you may have a thermocline in the deepest part of the pond, but you wont know until you get some graduated temp readings top to bottom. A pool thermometer, railroad spike and some nylon cord work well. You can adjust the depth by setting the weight on the bottom and adjust the depth of the thermometer to the depth you want to test. I would check every foot until you find the depth where the greatest temp change occurs. That's how deep your transition is. But that change may be minimal and may not leave your fish much area to escaped. Regardless, you may still need to change run times to early morning to keep from overheating the pond.

Again, they wont be able to live down there, but they can escape the warmer water temps for a short period.

.10 surface acre pond, 10.5 foot deep. SW LA. The epitome of a mutt pond. BG, LMB, GSF, RES, BH, Warmouth, Longear Sunfish, Gambusia,Mud Minnows, Crappie, and now shiners!!...I subscribe!!