I purchased a UV sterilizer. It worked pretty well, although it took
about a week to clear up. I think I had a pretty large bloom because
I got a 25W sterilizer which is quite large for 46 gallons.
It might clear up faster if you use a flocculant. Something like Mardel's
Brite N Clear, that causes particles to clump together so they can be removed
by the filter. IME, the combination of UV sterilizer + flocculant can clear
greenwater over night.
Leigh
http://www.fortunecity.com/lavender/halloween/881/