That's kind of what I was thinking - not looking to get a ton of flow out of the return pump(s), just enough to turn over the tank water and leave the circulation to the closed loop.
After seeing Eric's (can't recall last name, lives in north Nashua/Merrimack) tank with his sump in the basement, the water coming down through the tank drain had enough push and durso bubbles that the first section of his sump was practically working as a skimmer by itself. I think I'll try to feed the skimmer directly from the drain and either tap into the return or use an Aqualifter for the Ca reactor feed, effectively eliminating another pump in the basement. I like the idea of jamming the water skimmed from the top of the main tank directly into the skimmer as well.
I'll modify the schematic.