Pool and Spa Issues Glossary of Terms


An electrochemical reaction causing a black stain normally found around metal fixtures or on the pool finish. It is caused by two dissimilar metals being plumbed together or from an improper electrical grounding of pool equipment or lights. Electrolysis also means the decomposition of water and other inorganic compounds in aqueous solution by means of electricity. Chlorine generators use this principle to produce chlorine from salt in the water.


A unit of length equal to 1 millionth of a meter – it is .000394 of an inch. Microns are used to describe the pore size of filter media. Sand filters have openings of 25 to 30 microns; cartridge filters have openings of 8 to 10 microns; and D.E. (diatomaceous earth) filters have openings of 1 to 5 microns. Humans, without magnification, can see objects 35 microns or larger. A granule of table salt is between 90 to 110 microns.