Swimming Pool Terms Glossary



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Backfill Dirt or other material used to fill in the area or gaps between the pool or spa walls and the surrounding excavation.

Backflow The backing up of water through a pipe in the direction opposite to normal flow.

Back Pressure Resistance to flow, normally expressed in pounds per square inch (psi).

Backwash The process of thoroughly cleaning the filter by reversing the flow of water through it with the dirt and rinse water going to waste.

Backwash Rate The rate of flow through the filter media during the backwash cycle, measured in US GPM/Sq. Ft. (gallons per minute per square foot).

Bacteria Single-celled microorganisms of various forms some of which are undesirable or potentially disease causing. Bacteria are controlled by chlorine, bromine or other sanitizing and disinfecting agents.

Baffle A deflector plate on the inlet of a typical filter that disperses the water over the top of the filter bed or media more evenly.

Baking Soda See sodium bicarbonate

Balanced Water The correct ratio of mineral content, pH and alkalinity levels that prevents the water from being corrosive or scale forming.

Ball Valve A simple non-return valve consisting of a ball resting on a cylindrical seat within a liquid passageway.

Base – also basic – Chemical substance that releases hydroxyl ions ()when dissolved in water. A class of compounds which will react with an acid to give a salt. A reaction between an acid and a base is called a neutralization. Kind of the opposite of an acid. All liquids with a pH more than 7.0 are basic or base.

Base Demand The amount of base required to bring low pH and total alkalinity up to their proper levels. Determined by the Base Demand Test.

Base Demand Test A measurement indicating the amount of alkaline material required to raise the pH and alkalinity to their proper levels.

Basic Usually refers to water or a substance that has a pH higher than 7.0.

Bicarbonate of Soda See Sodium bicarbonate

Black Algae A really tough strain of algae that grows in pools and spas. It can be difficult to get rid of. See algae.

Bleach This term usually refers to liquid chlorine (sodium hypochlorite, NaOCl, 10 to 12% chlorine by weight). It is the same chemical used in laundry bleach but pool chlorine is 12% available chlorine while laundry bleach is about 5-6% available chlorine. A gallon of liquid chlorine contains about 1 pound of pure chlorine or is equivalent to 1 pound of gas chlorine.

Bleed To remove air from a pipe or device, allowing water to fill the space.

Bleeder Valve A device, usually on a filter, that allows air to be vented from the plumbing system.

Blower An electrical device that produces a continuous rush of air to create the optimal bubbling effect in a spa, hot tub or whirlpool. It is usually plumbed in with the hydrotherapy jets or to a separate bubbler ring.

Body Oil Term used to describe oil from or on our bodies that gets into the water. Sometimes it refers to sun tan oil or lotion.

Bond Beam The top of a wall of a pool or spa that is built stronger than the wall so it will support the coping and surrounding deck.

Booster Pump A water pump added to a spa circulation system to add pressure to the jets. Also used for some automatic pool cleaners.

Brass A metal alloy of copper, zinc and usually some lead. Brass is harder and stronger than copper because of its zinc content.

Breakpoint Chlorination The process of adding sufficient free available chlorine to completely oxidize all organic matter and ammonia or nitrogen compounds. All chlorine added after that point is free available chlorine. Requires a ratio of chlorine to ammonia of 7.6:1 but it is easier and leaves a chlorine residual to multiply the combined chlorine or ammonia content by 10 and add that as free chlorine to reach breakpoint.

Bridging A condition that exists when DE (diatomaceous earth) and suspended particles (dirt) closes the intended gaps between the filter and the filter grids in a DE filter which reduces the water flow rate through the filter.

Broadcast A method of applying chemicals to water by spreading them uniformly over the water’s surface.

Bromamines By-products formed when bromine reacts with swimmer waste (perspiration or urine), nitrogen or fertilizer. Bromamines are active disinfectants and do not smell, although, high levels are body irritants. Bromamines are removed by superchlorination or shock treating

Bromide Common term for a bromide salt (usually sodium bromide – NaBr) used to supply bromide ions to the water so they may be oxidized or changed into hypobromous acid, the killing form of bromine.)

Bromine A common name for a chemical compound containing bromine that is used as a disinfectant to destroy bacteria and algae in swimming pools and spas. Available as a tablet or as sodium bromide, a granular salt.

Bromine Tablets Common name for two chemical compounds containing bromine. They are used as disinfectants to destroy bacteria and algae. A separate oxidizer must be used to destroy swimmer waste. (Leslie’s Bromine Tablets)

Brominator A mechanical or electrical device for dispensing bromine at a controlled rate. Most often a canister or floater filled with tablets of bromine.

Bronze Any of various copper-based metal alloys that may or may not include tin, lead, or other metals in small amounts.

Brown algae A particularly hardy kind of algae that can look brown but is actually what is called yellow or mustard algae. See algae.

Brush Usually refers to a special underwater brush that attaches to the end of a telepole used for sweeping debris from the bottom of the pool or spa.

BTU Acronym for British Thermal Unit. The amount of heat necessary to raise one pound of water one degree Fahrenheit.

Buffer A substance or compound that stabilizes the pH value of a solution. It is also the water's resistance to change in pH.

Bypass An arrangement of pipes, gates and valves by which the flow of water may be passed around a piece of equipment or diverted to another piece of equipment; a controlled diversion.

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