Bacteria produce enzymes that allow them to break up complex compounds into pieces that can enter the cell to be used for growth and reproduction. Some bacteria use the carbohydrates and proteins usually found in the suspended solids that elevate biochemical oxygen demand (BOD), while others employ compounds most organisms cannot, such as sulfide, ammonia and hydrocarbons. When added to water, the bacteria attach themselves to solid particles, whether floating in the water or settled on the bottom, and secrete enzymes which decompose the particles. Certain dissolved compounds, such as ammonia and sulfide, are absorbed directly into the cell. Combinations of species often provide a more powerful and complete degradation of specific pollutants than individual strains applied alone, because the by-products of one species often serve as another species' food. Only a correctly balanced formula of bacterial strains, such as Clear-Flo, Enz-Odor, Nu-Bind and Treat-A-Loo formulas, can use this synergistic effect to completely break down pollutants to non-toxic by-products such as carbon dioxide, water and sulfate.