Bottom line: higher dosage levels like 90,000 microwatts (less flow) for protozoa treatment, lower dosage levels 35-45,000 microwatts (more flow) for reef health.
There is another thread here that may be helpful that @ichthyoid started here:
A few considerations when sizing a UV (please don't stone me, until reading ;)
So, you've heard about, read about & discussed getting a UV for your salt water aquarium. Great! Before you go buy the biggest, baddest electronic parasite sledge hammer money can buy, you might consider what it really takes to do the job. I controlled parasites in a 55 gallon with 15 watt & 150...
atlantareefclub.org
You can read and research more once you have the UV going and make adjustments from there.