First I'll start by saying I like this skimmer, only had it a month or so but so far it's been great (aside from the odd issue I'm having). When run @ 9.5" depth the I can set it to about 3- 4 turns from fully open on the water level & .5 - .75 on the air knob. Works great, moderately wet skim. Here's the issue - If I so much as move the skimmer up 1/4" in depth I can barely get it to skim, it is very dry (more on the neck & lid than anything else). This is with the water set @ max closed (just at the point where the threads engage). I've tried the air @ most all settings. It still seems to prefer .75 to 1 open. Any more and it just gets larger bubbles lower in the body = less production. I know what the thought would be........then don't raise it up ........well that brings me to the only flaw in the design - the drain. The straight down tube fitting doesn't really work for me (or for who I'd ask?). My sump is 16" tall = I need to raise it up a tad to use the drain (plan is to drill out the fitting & tap it for a 1/4" npt x 90*). I first tried it raised 1/2" that didn't work at all, so I dropped it to 1/4" (just a single piece of acrylic)..........hasn't worked that well so far. It seems very odd to me that 9.5" depth = 3 - 4 turns from full open & 1/4 shallower (fully closed, like 12 turns) = minimal skimming?????? The real reason I want to use the drain is so I can fit a neck cleaner - it seems performance drops fast as the neck gets dirty. At the 9.5" depth I'll get 1/2" of skimmate on the 1st day, then it's 1/4" over the next 2 days..............clean the neck & it's back to 1/2" in 24hrs. Happy I found this forum - I was nearing the point where I'd have to say "nice skimmer, just doesn't work in my application".