TIPS: setting the ASM skimmers for, well, skimming
1) wet skimming (looks like weak coffee)
set the bubbles in the collection tube, inside the collection cup, to 1" from the top of the tube. Sit back and wait, it will produce very wet foam.
2) dry foam ( will produce very dark smelly skimmate)
set the bubbles to the bottom of the collection tube inside the collection cup. Production will be much slower, removing more organics and less saltwater/trace elements.
What setting should you use? For the most part, produce the thick dry foam. If you just blew off your rocks, stirred your sand, or the water looks a bit yellow/floaties - increase the rate of production for a day or so to clean things up a bit.
The goal should be to remove enough to keep your system healthy, but also keep your corals and macro fed with some organics. These skimmers are very good and can actually overskim fairly easily. Over skimming requires weekly water changes of at least 10%.
Disclaimer: These are not scientific facts - but I did sleep in a holiday inn last night
