you can say bigals, lots of people link to them. A skimmer will help to reduce the algae in your tank. How so?
The nutrience that algae needs to grow is attracted to air. So what a protein skimmer does is bring tank water in, and then inject micro bubbles into a cylender that will force the water to be exposed with the bubbles. These bubbles will then take the nutrience that algae thrives on, and will deposit it in the collection chamber.
When all is working well, the chamber should have some water, but a ton of bubbles. The more bubbles, and the longer the expousure time, the better off you are.
BUT, skimmers are used mostly with marine tanks, for they are a whole lot less tolerant of algae (from what i read).
http://youtube.com/watch?v=rSNePdM_zGI check out the video there... Try to ignore (what i think) are hallide lights, they are bright, but you can see the skimmer working. It almost looks like a Berlin.