My Prizm didn't work at all for me....after 4 months I got rid of it and bought a Coralife Super Skimmer. It is 10 times better than the prizm ever was. I would advise anyone against getting a prizm, but that is just my opinion. I would suggest a Coralife to anyone looking for a good skimmer for not a lot of money.
I think they're hit or miss. On my 65g I'm getting a fair bit of disgusting-smelling skimmate, and the Prizm needs next to no adjusting. On my 30g I fiddled with it a lot and no matter what I did, I never got anything close to what I'm seeing now - it pulled a lot of watery, lighter coloured skimmate and now I see thick, nasty stuff floating in almost black liquid.
I also think that is the key, instead of changing it every day just leave the thing and let it do it's work. The only problem with mine is the noise, and it is impossible to sleep with it on so i turn it right down at night.