....it gets the surface of the water to fall into the skimmer. and, it makes your skimmer more effective.
...it's not a symptom of anything wrong with your tank. While not good, it is simply a biproduct of your tank/filter design.
It's yet another reason why sumps are so popular. Water falls into the sump from the surface of the tank taking this oil with it.
40 Gal Hex, 10 Gal Sump, CPR overflow with Mag 7 return, Maxxima 35 RO
, 10K MH
pendant, 2 x 15W actinic, 1 yellow tail damsel, 1 high fin goby, 40lbs LR
.com rock, 1 red head goby, 1 algae blenny, Leather, blastomussa, sun, and hammer corals, green polyps, carpet anemone, 2 sexy shrimp...and more LR
critters than you could imagine in your worst nightmares.... Mantis in 5 gal