sounds good.
I strongly suggest using 10 gph per 1 W of UV, or 250 gph of water flow through a 25 UV.
I would assume your return pump is larger than this so you would want to either A) use a separate pump to either pump water back to the main tank or back to sump itself, or B) use a T fitting and ball valve in the return line from your main pump so you can flow only 250 gph through the UV.