The concentration of DOC in aquarium water has a major factor in the skimmer’s performance. It is easier to separate something from water with a higher concentration than water with low DOC. Basically the skimmer can only pull out what is present in the water pulled in by the skimmer pump. The skimmate collection, color and concentration is dependent of what is fed to the tank, the bio-load and the setting of the skimmer. To adjust a skimmer properly users must be patience and regulate it several times over a period of a few days. Also note that new plumbing and equipment will introduce oils within the water which will have an effect on the foam production of the skimmer.