I did aero/nft for over a year and struggled with water temps in the summer.. Problem you'll get is root rot, and believe me, when an aero system goes south, it can happen fast. Some frozen 2L jugs will help, but it's a maintenance pain.. If you can, try to get your space to the upper 70s with the lights on. Everything will be happier.

One other thought on the res.. how about replacing your chiller with a larger unit? Pricey, but your problem would be solved. Make sure to match the pump properly too.

Last.. I wouldn't risk your root zone growth over having higher temps to promote vegetative growth.. My 2 cents.

Good luck!

Peace, Farmer Rich