I defined that using your own statement. "Going from .2 to .1 is a huge change" That certainly seems "good". Well beyond good. Yes / No / Yes. Sentence 1/3) I guess I was not clear on the sample rate. You clean the screen every week. So the number I am talking about is a period of one week. Sentence 2) No. You cannot use actual level changes as a measure of "good", because that then is a statement also about the INPUT of PO4 into the system.. To the extreme : If you continually pour plant fertilizer in the tank, the ATS will not keep up, but it still can be removing PO4 like crazy. Does that make it bad or good? - An impossible question. No, it CAN still be good, just not good enough to control a completely out of whack tank. Seriously : You are asking me to prove it is miraculously good. I think you are too used to the over-hype? ??? Algae grows, using phosphate from tank -> algae removed = phosphate removed.