how long does a uv sterilizer take to work?

[ws66370]

i bought this uv sterilizer in the 7w version:
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+4393+16748&pcatid=16748

I bought it to combat green water in my 29 gallon planted tank that i have tried everything to get rid of. i hooked it up yesterday afternoon and expected to wake up to clear water but the water is still green... am i missing something?

 

[jmhart]

It should take about 24-48 hours to kill all of the free floating bacteria. Even after that, the water will still be brownish-green(free floating dead algae). Give the UV 24-48 hours, and then do a 50% water change to help pull out the dead stuff. If you have any kind of micron filter, you can hook that up and it'll help remove the dead algae.