I'm trying to recall my research from a few years back.
If you're just using for clarifying (reducing waterborne algae) almost any sterilizer will do. It doesn't take much to clarify. If you're looking for sterilization, then there is an ideal flow rate and size to look for.
Generally 2-3x turnover an hour (just a recommendation as I haven't ever seen anything published repeating this) and an irradiance level of 320,000 uw/cm2 according to the University of Florida recommendation for killing marine protists (aka ich).
Most of the time, that put the flow around 250-300 gph through the sterilizer.
What was interesting was I found the UV placement much more successful when I ran it with the intake towards the bottom of the display tank behind a rock somewhere and not placed in the sump... Which unfortunately can be a pain to achieve without tubing/piping everywhere and the UV placed above the display. Freshly hatched and actively foraging ich theronts tend to be in the lower levels of the water column so it makes sense for placement of the UV intake water.
I would skip the coralife. I'm unaware if they use UV resistant plastic or publish their irradiance levels.
@steveb I'm still using the TMC unit but may be upgrading this year to the Pentair (emperor) 150 unit with my increased water volume.