I got the same one (NW-150?) for a customer tank and it started producing skimmate within a few days, but that tank was very dirty. The scum buildup means it's working, but you might need to rotate the outflow tube a few millimeters so that it starts flowing. During the break-period the adjustments will just make a short-term difference. Sump level does make an impact. If you wait until it's ready for a top-off, and pay attention to the bubble level, as you add water you can see the bubbles rise by the same amount. So if you top it off and set it so that it's producing good skim, by the time your sump lowers due to evap, the skim production will be reduced. I would adjust it and check it 10-30 minutes later, if it's frothing over sticky leave it, if it's frothing over and skim is clear, dial it back slightly, if it's nothing then close it up slightly. Don't adjust more than once a day. After 2 weeks, get your sump at the desired level, mark it on the glass, set the skimmer, and top off a couple times a day to maintain the sump level so you can tune in the skimmer. Make adjustments only once or twice a day, ad with that skimmer you should be able to find the happy spot easily and just leave it, then top off daily. Or you could set the sump about 1/2 way between max and min and use that to set it up for medium skimming, fill it up and monitor skim production as the sump level drops to minimum, but that's only if you don't want to top it off every day. And I would still top off every other day.
