I really appreciate the time you are taking to reply to me. I'll try to see if I can replace my plumbing with 1.25" unfortunately that size ain't so common where I live. Maybe I'll sell the UV unit and get the pro max 55W if getting the proper flow rate is too much of a hassle. Time to redesign plumbingUpsize your return plumbing if it's feasible to do so. Eliminate as many 90's as possible. Run 1.25" all the way and reduce it at the last minute (aka, right before the return bulkhead). That will provide a significant increase in flow from the pump and reduce the contact time.
I'd run the UV on the main pump - full time. Turning it on and off is no bueno, so leave it on. Get yourself a bucket and calculate your GPH to see where you're at once it's all plumbed up. If it's lower than what you're comfortable with, you may need to upsize the return pump. I know the doc says 45,000 max for reef, I have run 60,000 without any obvious issues. When I had dinos and was running >100,000 - I had zero pods in the tank - it was... well... sterile.
Take a look at my build thread - I think page 2 or so. I detail the plumbing design and explain what I'm trying to achieve with it. I ran all 1.25" pipe as far as I could. If you go any larger than 1.25", you then have other challenges because the weight of the water in the pipe starts to work against you.