I have set up many skimmers. I got out for 7 years..I spent 2 hours trying find out why this damm skimmer was 100% on air until I remember you need a gate valve. DUH....still the worng skimmer for this tank methinks ( new one arrives Thursday) but even the best forget the 101 stuff! A valve on air input allowed me to at least control and dial in.... I am getting old!