The goal is to not have ANY bubbles that are being sent back into your tank. The water flowing from you skimmer back into your tank should be free, or nearly free, of bubbles. This is because the more bubbles that go into your tank, the less efficient it is. The whole concept with the skimmer is that the stuff you're trying to get rid of (the extra protein, which comes from a number of things, like un-eaten food, fish waste, dead fish, etc.) "sticks" to the bubbles that are rising up through the water. So, the more bubbles you have rising up through the skimmer's cylinder (but not going into the tank) the better it's doing it's job. Your skimmer is not working as good as it should if you have alot of bubbles going into the tank. Just the opposite, in fact. With a large number of bubbles flowing back into your tank, your basically defeating the whole purpose of the skimmer in the first place, because a majority of the water flowing back into your tank is "unskimmed." Adjust your airflow intake until you don't see any bubbles, or very few. BTW, I run my skimmer 24/7, with good foam production. Good luck.