[inwall75]

I love my protein skimmer. You'll have to pry it out of my dead, cold hands. However, there is a limit to their effectiveness. Skimming can only remove hydrophobic (water hating) molecules. Unless you run your skimmate very wet, it will not remove hydrophillic (water loving) molecules.

Next to ozone and protein skimming, GAC (Granular Activated Carbon) is one of the most efficient ways of removing undesirable organics (both hydrophobic and hydrophillic) that make the water less clear like tannins, humic acid, etc. As Tom indicated, not only that, many softies exude various alleopathic compounds (chemical warfare substances) including terpenes which are fairly nasty to keep other corals from growing nearby. Some of these Terpenes are hydrophobic and can be skimmed out but others are hydrophillic and will merely accumulate over time and can only be removed with waterchanges and GAC. In some people's tanks, the accumulation of these hydrophillic terpenese are responsible for slowed growth in corals, death of corals, etc. That's why I advocate the use of both a protein skimmer AND GAC.