before to fix my self on one design I read and study everiting I could found on skimmer and get this conclusion
IMO the best and most advance skimmer is the Areofoamer 800 series
I use one that I made base on the same design for years and can't ask for more you can see pictuere of it on my web page
my ORP rarely drop under 400 and mostly alway around 410
here is a comparison
http://www.thereefweb.com/skimmer_comparison.htm