depends a lot on your res I'd say. some details may help. I hooked my chiller up to a 55 gallon res and recirculate there, but I was running a rdwc/ebb and flow kinda hybrid deal. I used flood table bulkheads and 3/4 inch pipe to 3/4 inch barbed fittings.I know you can't see any details there but one of the bulkheads has a piece of 3/4 inch tubing running to a pump at the bottom of the res, it just recirculates thru the chiller and back to the res. when I was running this system as hybrid rdwc/ebb and flow ( dunno wtf to call it actually) this worked well for me.