What kind of skimmer is it? The water flow should equal a minimum of 1 tank volume per hour, more is better, the air should be adjusted so that the bubbles in the water (rather than the foam that collects in the cup) are just at the base, to the beginning of the neck. In a new system you can expect a lighter effluent, as the DOC
is removed the skimmer will become more efficient and the foam should become darker. If the cup is overflowing with bubbles and it is breaking dow to a clear fluid, back down the air some. If the foam, never actually makes it to the cup...increase the air flow.