Also I just skimmed briefly through the article Len posted and one thing confuses me... well first the "4 different technologies" don't seem that much different from one another but in the conclusions he states
These tests revealed that there was no demonstrable difference between the Euroreef CS80 needlewheel skimmer, the Precision Marine ES100 venturi skimmer, the Precision Marine AP624 airstone skimmer, and the ETSS evolution 500 downdraft skimmer with respect to the rate constant for either TOC or BSA removal.
But in his data he shows the ER CS80 removes 56 +/- 15 % of the BSA, where as the PM Airstone removes 95 +/- 5% of the BSA which to me sounds like a huge f'ing difference, although the "rate constant" (which I still haven't grasped) is comparable, to me the data shows one skimmer removes just about everything, where as the other removes half to two thirds.