There are many types of chemical media on the market today. GAC has many uses and should be a part of your filtration methods. An article in Aquarium Frontiers by Dr. Craig Bingman showed that the use of GAC has a dramatic effect on the light spectrum that reaches different depths in the aquarium. GAC also pulls many toxins that cannot be otherwised removed, heavy metals, phenols and the toxins put out by various corals. There is also a down side, GAC will also remove beneficial elements such as iodine.
Phosphate sponge is another popular media that is very useful.