<< should answer most of your questions about protien skimmers and skimming.
and if i bought one now can i use it in my freshwatter tank? i got a really messy 13 inch pleco
I have only seen skimmers work in FW
dirty tanks, or tanks with alot of yellowing agents, like lots of driftwood, etc.. Even in those tanks there is not enough surface tension on the bubbles for efficient and effective skimming, for the most part they are useless on FW