's is what you have. Dissolved Organic Compounds. A protien skimmer with a surface skimmer will remove it. There are three dangers with excessive DOC
's. 1) It can limit the gas exchange at the water surface and lower the O2
content in the tank.
2) If it gets heavy enough, it can block enough light to have an adverse effect on photosynthetic inverts.
3) It is composed of nutrients and stuff that will break down into nutrients. As you probably already know, excessive nutrients in the water will likely fuel an outbreak of pest organisms such as hair algae, bubble algae (valonia), and aiptasia anemones.