you dont have to buy them you just make them i found out you can buy one but thee like 50us you can build them for about 2$ cdn.
These things look great they can increase the flow buy large amounts out of returns and closed loops.
here are some links
http://www.thereeftank.com/forums/sh...threadid=23330
http://www.thereeftank.com/forums/sh...r&pagenumber=1
i am going to build this skimmer soon and will keep you posted