It'll kill algae in the water like no ones business. Set it up for a slow flow. don't put 900gph through it lol. But it won't effect algae on glass etc.
yes the lower wattage the slower rate you want going threw it so it has time to kill it. i'd go with like 30 gph just to be safe. maybe lower. but don't listen to me i have never used one.
I bought a cheap 24 watt one at petsmart for my 135. In less then one day it went from
being very cloudy to clear. Lools like my fish are floating in air lol