Does your skimmer overflow all the time, or does it stop after a while?
If it stops after a while, does it start to overflow after you feed the fish and/or corals in the aquarium? If so, maybe the type of food you are using is causing your skimmer to overflow.
I use the AquaC 400 skimmer on my tank, and it starts to overflow for a few hours after I feed my fish with frozen Ocean Nutrition Fomula 2. It does not happen with any other food (
frozen or dry) that I use.
If your skimmer begins to overflow after feeding, try changing the food you use to see if that is the cause.
Good Luck And Have Fun!!!;