Just run off your COR20 as recommended typically by UV makers, you can bypass and service your UV anytime. Personally, I've added a flow sensor after the UV to dial it in.I'm trying to figure out how to plumb a uv my self. My tank only has one return hole drilled in the bottom of it. I'm thinking of running 2 pumps (cor20 for main tank and cor15 for UV) can I run it like this pic or will I have back flow issues.