[pogodzib]

Protein skimmers pull out whatever molecules attract to the air/water interface within the skimmer, so yes, just saying they only pull out organics is a misconception.

Here's a couple good articles if you want to get into it farther.

General: Protein skimmer - Wikipedia, the free encyclopedia

Skimmate Contents: Down the Drain, Exports from Reef Aquaria by Ronald L. Shimek, Ph.D. - Reefkeeping.com