Unless im reading it wrong, I dont think it will work. Basically you are pumping water into the powerfilter, draining it into the sump, and pumping it back.
I think you will either
A) Flood the sump
B) Run the sump dry and possibly burn up your pump
If your power filter pumps 200gph, and drains the same, but your return pump only pumps 150, you will flood your sump, unless you have a way to shut off the drain to the sump at a certain level. On the other hand, if your return pump flows 250gph, you will pump out more than your putttin in, and run the sump dry. It will be hard to match the pumps either way, and I think it would require constant adjusting, which IMO isnt worth it.
I think you would be better off, getting a small over flow box, or getting your tank drilled with an internal overflow box for more reliabiltiy.
cs
50gal cube in the works.
2x250w Coralvue eballast and reeflux bulbs for sale.