Solids can be dispersed in swimming pool water in several forms. The nature of such dispersions depends on the size of the particles. In general these floating or suspended solids (up to 0.001 mm in size) can be removed from the pool water with effective filter systems. Each person entering a swimming pool introduces colloidal impurities such as bacteria, germs, cosmetic residues, body oils and perspiration into the water. Those substances, sized between 0.1 and 0.001 microns, are dispersed in the pool water and are not directly visible to the human eye.
However, such contamination may be visible with the use of underwater spotlights, revealing turbidity. This contamination cannot be removed completely even by highly effective filtration technology, which can result in an increase of combined chlorine, leading to an organic overload in the pool.
The use of flocculants will cause dirt particles to clump together so that they can be retained in the filter system. Aluminum and iron salts are commonly used in a flocculant so that the insoluble aluminum hydroxide forms a floc precipitate responsible for colloid removal in the wastewater.