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I'm still testing my DIY Air Driven HOB skimmer. During the first test, the water coming into the skimmer was overflowing out of the collection cup...it wasn't leaving the skimmer fast enough. The piping that sent the water back to the aquarium was 1/2" sch 40 PVC. The responses I got from my original post mentioned increasing the return pipe to 3/4" and lowering the point where the pipe spills back into the tank. Well, I did all that and it worked no more overflow. No I want to know if the level in the skimmer column is high enough. Also, I tested the air portion of the skimmer with my small Whisper 500 air pump. The pump did not have the power to generate the magnitued of bubbles required. Can anyone suggest a good strong (and quite) air pump that would do the trick? The skimmer will hang off the back of the aquarium and the air pump will be on the ground or very close to the ground. The point were the air enters the skimmer will be approx. 52" from the air pump. Here are two pictures of the skimmer. One shows it in operation on my test tank and the other shows the water level in the column while it's operating.

Thanks for any input.