From one vendor's website:
* TITANIUM HEAT EXCHANGER� for maximum salt water corrosion protection
* Only unit on the market currently which utilizes super high efficient UL/CE ROTARY compressor
* Quieter than 9 out of 10 chillers on the market. Rotary compressor is extremely quiet!
* Drops 80 gallon typical tank 10 degrees.
* Digital Temperature control
* LCD displays water temperature
* R134a Refrigerant
* Recommended 100-400GPH flow
* Dimensions 360x208x266mm LxWxH
* 5/8" barbed Inlet/Outlet
* 5/8" Tubing included!
* 120V 60Hz operation
* 1 year manufacturer warranty
Based on the info you gave me over the phone (4' of head, 1" tubing, guessing about a 6' run), your head losses should be around 10' or less, which, with a Mag7, would give you a flow of 150-200 gph, just about right.
You'll want to set the chiller temperature a degree or two above your heater temperature so the heater and chiller aren't "battling" each other. I'd put the Mag7 in the sump, plumb it through the chiller and into the tank, and don't forget to add a siphon break or check valve to prevent back siphoning in the event of a power outage. That should take care of it. HTH. I'd offer to help but I'm leaving town in the a.m.
Dave