Swimming Pool Terms Glossary
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Main Drain Usually refers to a plumbing fitting installed on the suction side of the pump in pools, spas and hot tubs. Sometimes called the drain and is located in the deepest part of the pool, spa or hot tub. It is not a drain such as a drain on a kitchen sink. Main drains do not allow the water to drain to waste but rather connect to the pump for circulation and filtration.
Make-Up Water Sometimes called "tap" or "refill" water. It is the water used to replace water lost to evaporation, splash out, leaks or swimmer drag out in the pool.
Manganese (Mn) An element on the Periodic Table. Symbol Mn. Sometimes found in ground or surface water usually in combination with iron. Manganese is noticeable because it causes black staining when concentration is greater than 0.05 ppm.
Manifold The branch pipe arrangement that connects several input pipes into one chamber or one chamber into several output pipes. A filter manifold connects several input pipes from the filter septa back into one common pipe.
Mechanical Seal A mechanical device or assembly that forms a seal between a pump casing and a rotating shaft to prevent leakage along the shaft.
Media A selected group of materials used in filters and filter devices to form barriers to the passage of certain solids or molecules that are suspended or dissolved in water. Media is the plural form of medium and refers to more than one type of barrier material. In the pool and spa industry, filters use either sand, polyester or diatomaceous earth (D.E.) as the media.
Metal An element that forms positive ions when its compounds are in solution and for which the oxides form hydroxides rather than acids with water. Most metals are crystalline solids with metallic luster, are conductors of electricity, and have rather high chemical activity. Some metals are quite toxic.
Micron A unit of length equal to one millionth of a meter -- it is .0000394 inch. Microns are used to describe the pore size of filter media. Sand filters have openings of 25-30 microns; cartridge filters have openings of 8-10 microns; and D.E. (diatomaceous earth) filters have openings of 1-3 microns. Humans, without magnification, can see objects 35 microns or larger. A granule of table salt is between 90 and 110 microns. Abbreviated as m m.
Microorganism Microscopic organisms, either plant or animal, invisible to or barely visible to the naked eye. Examples are bacteria, algae, fungi and virus.
Millivolt A unit of electrical measurement equal to 1/1000th of a volt. Abbreviated as mV.
Monopersulfate See potassium peroxymonosulfate.
MPS Abbreviation for monopersulfate.
Multiport Valve – also called a rotary-type backwash valve – This valve replaces as many as six regular gate valves. Water from the pump can be diverted for various functions by merely turning the valve. The water may be sent to waste, used for backwashing, bypassing the filter for maximum circulation, normal filtration, filter to waste (rinse) or the valve may be closed to pass no water.
Muriatic Acid 31.45% hydrochloric acid, chemical formula HCl. An acid used to reduce the pH and alkalinity levels in pool water. It is also used in acid washing, a process that removes stains and scale from pool plaster.
Mustard Algae A particularly hardy form of algae that is yellow colored. See algae.
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