THe fission skimmer sucks.......kinda.
I had it in my 20h and only ran it at night due to all of the micro bubbles, and i NEVER got skimmate once.
I'm upgrading to a 40 gallon cube, so all of my water and rock is in a rubbermaid tub waiting for the new cube to ship in. I said what the hell and threw in the fission. For some reason, the thing is going nuts with skimmate. I've got a cup full every day now.
I'm still going to upgrade though, as overall i'm not impressed.