I'll let the experts chime in with advice, I just can tell you what happened in my pond 2 years ago. My pond depth is about the same as yours, and I had RBT in it.

Water temps hit 70°F at the surface. Bottom temp was still in the lower 60's. The trout seemed happy. I turned on the bottom aeration system, only running it at night, or when the air temp was below 70°F. The pond started dropping due to no rain, and higher temps. Surface water temps started to climb to upper 70's. I started up the well, pumping 54°F water into the pond. Still kept with the aeration schedule. I started to notice the trout by the water going into the pond from the well. Within 2 weeks all the trout were gone. Water temps were above 70°F from top to bottom, even tho I was still only aerating when air temps were below 70°F. I can only summise that the diffuser in the deepest part of the pond mixed the whole water column (like it is supposed to) and there wasn't enough O2 in the warmer water for the trout. (no dissolved O2 readings were taken)

So, it's a combination of things that the trout need. Enough O2 to survive, and cool enough water. Just having cool water won't be enough.

But, if the trout made it thru the summer last year without aeration, then they might do the same this year.

www.hoosierpondpros.com


http://www.pondboss.com/subscribe.asp?c=4
3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).