If allowed to decompose the organics will fuel the activity of many unwanted microorganisms in the aquarium, increasing the total oxygen demand (BOD, COD) which will cause a reduction in Redox potential, as well as causing excessive production of CO₂ by bacterial respiration, which will reduce pH.

Furthermore, there will be an increase in nitrogenous and phosphorus compounds, encouraging growth of nuisance bacteria and eventually of nuisance algae. The accumulating organics also has a significant effect on light penetration, especially in the blue and near UV spectrum that stimulates coral growth.

Stripping out the organics from the water is therefore crucial for the success of the aquarium. Using strong protein skimming, fine mechanical filtration and healthy biological filtration (nitrification and de-nitrification) will treat the large organic particles and the end products of the organic decomposition processes. However, there are many small organic particles that can only be treated by very fine mechanical micro-filtration using activated Carbon.

How does activated Carbon filter water?

Scientifically speaking, Carbon removes the organics from water by a physical process called adsorption. Within a reef aquarium, the submicroscopic pores of activated Carbon is the final stage of the mechanical filtration process, adsorbing the organic molecules that are too small to be removed by even the finest mechanical filters or physically removed from the water by protein skimming.

Adsorption can be thought of as the adhesion of a molecule to surface by attractive forces. This occurs within the submicroscopic pores of the Carbon because the attractive forces between the organic molecules and the internal surfaces of the Carbon are far greater than the attractive forces that keep them dissolved in solution. This will continue until all of the surface area inside the Carbon is used up and it becomes saturated with organics.

What is activated Carbon?

Activated Carbon is an extremely porous material with a sponge like structure but with a very large internal surface area relative to its physical size. It is produced from many organic materials that have a high Carbon content such as coconuts shells, nutshells, lignite, bituminous coal or anthracite. The Carbon-based material is “activated” through physical modification and thermal decomposition in a furnace, under a controlled atmosphere and temperature.

The activation process significantly increases the surface area per unit volume of a fine network of submicroscopic pores which is what gives activated Carbon its ability to act as a filter material. The specific source of the Carbon and the specific activation process determines the physical characteristics of the finished product. There are many different grades of activated Carbon, and therefore they must be selected specifically for each and every application.