"Bob" wrote in message ...
I used to use one but haven't for a couple of years. I'm thinking about
it again. I have a 210 gallon reef . My primary interest is killing stray
pathogens. I'm thinking 40 watts and maybe 200 gallon/hour?

What "stray pathogens" you have on your mind?
This water flow is good enough to kill bacteria, algae
but to kill cilliates/prothozoans you need to slow down
to about 40 gph or even less for worms/crustaceans...