Morgan Lindster did an exposé on this product some years ago. I think it was posted on Inland Aquatics' website but alas they are not around anymore.
Basically it's PVC with what looks like shower curtain magnets (but they are supposed to be rare earth magnets), fastened to the inner PVC tube with electrical tape. Then another PVC sleeve over top of that, and a label and clear plastic tube over that. Throw in a couple of Jaco fittings so it can be plumbed up and, voilà! No more water changes.
Now - if you believe that, maybe we can talk about a bit of real estate I'm trying to sell...
Bottom line, if it sounds too good to be true, it usually is.
Bob Fenner posts about it too, here: http://www.wetwebmedia.com/algcontf15.htm">http://www.wetwebmedia.com/algcontf15.htm</a>
His words, "Snake oil". I've seen/heard many others call it just that too, and I concur.
I wish the page with the actual photos/description were still around...
Jenn