Not to push the thread but. . .I had the same issue until I got the flow right.
Too slow and algae was not affected. Based on the specs to kill algae and other
bad things i believe i have found a happy medium. For example - I used to get
algae on the glass at the output of the return nozzle - now I do not.

LeighMo wrote:

I disagree a bit. It will only kill free floating algae however if you clean
the plants, tank and rocks well new growth is cut way back

That has not been my experience. I had a UV sterilizer on my tank almost from
the beginning, before algae had a chance to get established. (It was to
prevent ich as I stocked the tank.) Nevertheless, as the weeks went on, I got
various algae infestations. IME, this is normal for a newly established tank,
and I didn't do anything special to control it, other than make sure I had
enough CO2 and fertilizer. Eventually, it went away on it own. However, I
still have more algae in the tank with the UV sterilizer than in the tank
without one. (Because the other tank has les slight, and lots of snails.)

Leigh

http://www.fortunecity.com/lavender/halloween/881/