Ok. I have an old reef dynamics skimmer. It runs on a brand new Rio 2100 pump with a venturi. So it has been running for 8-9 months and making skim. At its highest output I was emptying twice a week. Not a full or even a half cup but an inch or two of skimmate. I had a small grouper and some Triggers. I lost the grouper. I am also running two Aquaclear 110s because groupers are messy. Not too long ago the skimmer stopped making skim. I removed the pump and soaked in a vinegar water mix for 3 + hours just to be sure its not calcium. I did notice when I ran a diatom filter on the tank that the skimmer wouldn't work. I am wondering if my water is too clean for it to work. The pump still makes mircobubbles. Once in awhile they almost make it to the top. But its been a few weeks and no skim. But the other think is that recently I noticed hair algae blooms where I never had any. I have chaeto in the sump which is supposed to out compete the hair algae. But that is new and the tank is established.