a chiller would be real good, how you'd implement it on the res and a top off res I don't know, I'd just go with a huge cooler, they're actually pretty affordable and you can drop in some ice in a pinch with no chiller.
In a chiller I always recommend a drop in just because I like them so fucking much, no pump to heat water, it's counterproductive. Funny out of the 3 chillers I own only one is drop in, mainly due to price.