I swear by the uv sterilizer. Have one on 2 out of 4 tanks. Started using them 3 years ago....
You do NOT want to run it with your main filter. I have a separate powerhead just for it. It's aquaclear powerhead. Maybe 70gph...I have to check. But, I agree with the above poster. You want a slower flow for the uv light. It's like a microwave, zapping those lil particles. Longer they are exposed for, quicker they are gone.
When I first got a uv light, the water in my one tank was so dang green I couldn't see the fish, or tell if any were dead...not kidding. This was in my 125g, and I had some BIG pacus...The uv light started clearing it up one the first day. At the end of the 2nd day, I did a water change and crystal clear water since.
As for parasites...it is nice not having to quarantine any newbies, and I haven't had ICK for 3 yrs now. I just put the newbies right on in, and no worries.
It's good to replace the bulb every 12 months. At my lfs they are $25 each