Ugh. I fiddled with this skimmer for a long time before I finally just got rid of it. Even when u get fine bubbles skimate won't be what u think. :-/. Sorry to be buzz kill :-/
Has a 2 week break in time and if you bought it used then you might want to shake the pump and clean it well with vinegar. If not you need to do the airline mod as after that it works perfect and you have to keep the water line perfect for it to work properly
° The 9002 works best with the water about 1/2" to 3/4" below the water line marked on the front. So if the water is currently at that line, then the skimmer body should be raised up about .5-.75 inches.
° If the blue adjustment screw is difficult to reach because the skimmer is in a tight location, then the airline mod can make it easier to make adjustments. It does this just by relocating the adjustment screw to a spot that's easier to reach. Apart from that, it doesn't increase performance. Be careful that the airline does not draw air from directly above the water surface, as the salty water/air will quickly clog the Venturi.
° A constant water level is very important, so the 9002 should be used with an ATO or else put in a chambered area where the water level doesn't drop as water evaporates.
° Don't expect the 9002 to produce the thick, dense column of bubbles seen with full-size skimmers. It is not a needlewheel skimmer so the bubbles will never be as fine. However, this is not a bad thing. It doesn't mean it won't perform just as well as a larger skimmer. Because it doesn't have a needlewheel, the 9002 pump is much quieter and more efficient. It is fully capable of skimming water volumes up to its rating of about 50 gallons. Though a dense column of fine bubbles is often used as a way to judge larger skimmers in larger tanks, it just doesn't apply to these smaller Nano skimmers.
° In small aquariums, surface tension is affected much more by additives, feedings and putting your hands in the water. Changes in surface tension will change how the skimmer performs. In other words, you can expect a skimmer to be temporarily "inconvenienced" whenever you feed, use glue or epoxy or rearrange anything in the tank. Smaller volumes of water, like in smaller aquariums, are affected much more quickly by this. Larger aquariums have more water to dilute the effect.
° When you adjust the blue air screw, make small adjustments and wait a minimum of 24 hours before making another adjustment. Making many adjustments hours apart, or making adjustments after feeding or rearranging, can lead to a very frustrated aquarist.
I hope that helps some! Please let me know if you have any questions or thoughts...
Sorry. I always thought it should be run with the water at or above the line. Anytime my tank would evaporate ant the water would fall below the line, I wouldn't get any bubbles. Ill have to check it when I get home.