return pump question

[fast94m]

Seeing that my mag 9.5 is throttled down alot i figured im wasting energy/heat by using it as a return pump on my 75g rr tank. So i was thinking about downgrading to a mag 5 or 7. Would i notice a significant drop in water temperature? The overflow is split, 1/4 goin to my refugium and 3/4 about goin to my filter sock in the sump, the refuge overflows into my sump also where the mag returns the water. Would a eheim say 1260 run cooler then a mag 5 or 7 and alot cooler then a mag 9.5????? What is the rule of thumb for turnover in a sump again? I think my overflow is designed to handle 500-600gph, its a marineland jetstream tank with a custom pvc return, head on the pump is about 4 feet btw.

Any help is appreciated

[ChemE]

The rule of thumb is 3-5 tank volumes per hour through the skimmer/sump loop. If you are direct feeding 100% of your overflow water to the skimmer this drops to 1-1.5 tank volumes per hour. If you have chaeto to keep tumbling just stick a PH in your fuge, it works perfectly and takes far less energy than increasing the flowrate through the loop.

As for the pump itself, I use a MJ1200 on my 55 because I have 46" of hydrostatic head. The sump for the 190 that I'm planning will be elevated so that there is only 6" of hydrostatic head. I'll be using 2 MJ900's for the return pump there. I wouldn't be surprised if your water temp dropped a few degrees by ditching that 9.5 for a more reasonable pump.