Aquaponics. I need ideas and opinions.

I'm hoping to implement a full scale aquaponics set-up this fall. I want to grow 100-300 lbs of tilapia per year, and the poopy water they live in gets pumped around to plants in a hydroponic style system. The plants act as water filters, using the dirty water as nutients and then the cleaned water goes back into the fish pond.
Here is my main issue: temperature. Tilapia like water roughly 80-86 degrees. It's pretty easy to heat up water, but I can't figure out how to cool it down. My first idea was to put it in a greenhouse (which I'd have to build/buy) and use an evap to maintain temps, this seems expensive and I felt like there's probably a better way. I thought about burying a second reservoir tank-- a sort of geothermal idea, but I don't think the volume of water (somewhere between 100-500 gallons) will be great enough for that to have a significant impact. Do any of you have experience with ponds? I know they must work somehow because people out here have them... If the tank is in the ground and approx. 8' by 3' and 18" deep underneath a shade structure what kind of summertime temps do you think I'm looking at?
My final idea (for now) is to put the tanks in the converted garage building where I work which has the benefit of already having power and a cooling system, and have the piping go through the walls to a set-up outside which will basically be a lean-to style greenhouse/shade house (depending on the season).

The rest of my problems are mechanical and engineering related, as I have zero experience with this type of thing, but I figure they can probably be worked out in the couple of months I have before I have money saved up to begin...