In the Beginning:
Back when I first started keeping aquariums, there was rather limited access to different brands of products, and everything was rather “generic.” I remember one of my local stores raved about how shiny their carbon was compared to the pre-packed stuff. This was supposed to be a good thing. Only later did we realize that shiny “coal” was not very absorbent. Even the non-shiny (dull) carbon was not much better, as it was standard carbon and not the “activated” carbon we have today.
Dawn of a Revolution:
By the mid ‘70’s, we were having much better success keeping more and more types of fish. This created a demand for quality products, and several manufacturers jumped in to offer such products. One of the first really successful products was “activated” carbon, capable of removing more pollutants and lasting longer in our filters. The process of activating carbon can take several forms. Most begin by literally baking the carbon to very high temperatures (600-900F) to burn off the excess organic material trapped in the carbon structure. This opens up the pore structure of the carbon to offer a massive surface area per volume, up to 500 square meters per gram. This heat activation can leave behind a fair amount of inorganic ash that could cause problems in an aquarium. To eliminate this, the manufacturers will give the carbon a chemical (acid) wash to rinse out the excess ash. For some applications, the carbon is a powder, but this form is rarely used in aquariums. For aquariums, we use a granulated carbon or an extruded form. The extruded form (Lifegard Pelletized Carbon) will have less dust and more structural strength to work better in pressurized systems. The granular carbon (Black Diamond) is shifted through a wire mesh to get a more uniform size of granule (and to help eliminate some of the dust). Other granules are machined to a spherical shape (Matrix Carbon) to prevent packing of the carbon, allowing higher flow rates through the carbon. It would also work better in a fluidized system.
The New Age Arrives:
As we hobbyist became more discriminating in our choice of chemical media, a controversy about excess phosphate left in some of the activated carbons came to the forefront. We did not want this algae nutrient to be added to our aquariums. All carbon is organic based material that has been compressed for thousands of years, and all carbon will have some phosphate. The baking and acid wash will remove most of it, but to claim to be phosphate free is really more of a marketing statement than reality. Seachem does offer a product, SeaGel, which is a mix of activated carbon and phosphate removing media to make a “phosphate free” carbon. Others have taken to mixing the activated carbon with ion exchange resins and organic scavenging resins to eliminate the phosphate and other pollutants that the carbon might miss. Products like Chemi-Pure and Bio-Chem Zorb for marine or freshwater tanks are some examples. One advantage to the combinations is a longer useful life in the filter system, requiring less frequent replacement, which is great for canister filters. Our fish get the advantage of better water quality, and we get the advantage of less maintenance!