My coralife 220 skimmer has been working perfect. I added a small pouch of carbon to my sump this morning. About two hours later my skimmer collection cup was overflowing. Nothing else done to tank and skimmer was very steady.
Carbon does not ordinarily cause skimmate increase. Carbon always has a lot of dust in it that needs to be rinsed off before putting it in the tank. If you didn't rinse out all the dust, it could affect skimming.