ah ok, right.. i will test and see and adjust the water lvl accordingly. thanks !It's about how much water will drain back into the sump from the extra plumbing when the pumps are turned off, or when power goes out. You'll have to make sure your sump wont overflow from the extra water volume coming back down.
Since varios pumps don't produce a lot of pressure, I would go with the separate pump for the UV.
If you don't want any water to drain back into the sump from the uv/returns when you lose or kill power, you can get a one way check valve which will stop it.
These are the best ones...the price is pure ****, but they are pretty much a lifetime part.