Most of the waste from bacteria is in the dissolved chemical forms. Skimmers will only remove the bacteria, other organisms, suspended particles & partially decomposed bacteria. It is believed that skimmers will not remove the dissolved chemicals. The wastes from bacteria are used by other micro-organisms including different bacterial types until the dissolved organics can't be used any more by micro-organisms. Some of the bacterial wastes that are in the dissolved from will escape in gas form out of the aquarium.