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Swimming Pool Glossary


ACID: A chemical substance containing hydrogen with the ability to neutralise alkaline materials. Acid is used to lower the pH or total alkalinity of swimming pool water. Most common are hydrochloric acid (muriatic) and dry acid (sodium bisulfate).

ACID DEMAND: The amount of acid required to bring high pH or total alkalinity down to their proper levels. Determined by an acid demand test.

ACID DEMAND TEST: A reagent test usually used in conjunction with a pH test to determine the amount of acid needed to lower pH or total alkalinity.

ACID RAIN: Precipitation having a low pH value caused by air polluted with sulfur dioxide, carbon dioxide or nitrous oxide.


AIR-RELIEF VALVE: A manually operated valve located on the top of a filter tank for relieving the pressure inside the filter or for removing the air trapped inside the filter (bleeding the filter). Sometimes called a Pressure-Relief Valve.

ALGAE: Microscopic plant-like organisms that contain chlorophyll. Algae are nourished by carbon dioxide (CO2) and use sunlight to carry out photosynthesis. They find their way into the pool by rain or wind and grow in colonies, resulting in algae blooms. Algae do not cause disease, but provide an ideal substrate for bacteria to thrive in. There are over 21,000 known species of algae. The most common pool types are black algae, blue-green algae, green algae and mustard algae. Pink algae or red algae-like organisms can be found, but are in fact bacteria. Maintaining proper sanitiser levels, shock treatments and superchlorination will help to prevent or destroy algae.

ALGAECIDE: Meaning to kill algae. Algaecides perform best as a backup to a routine sanitation program. They also help to kill airborne spores as they blow into the pool. A variety of algae treatment products are available including copper and silver compounds, quat compounds, chlorine enhancers and herbicides. Algaecides are often formulated for a specific type of algae (green algae, mustard algae, black algae) with black algae being the hardest to treat.

ALGAESTAT: An algaecide kills algae, while an algaestat retards and prevents its development and growth.

ALGEA: See Algae

ALGICIDE: See Algaecide

ALKALI: Also called a Base. An alkali is the opposite of acid and is used to increase the pH or total alkalinity of swimming pool water. Most common are sodium carbonate or sodium hydroxide to increase pH, and sodium bicarbonate to increase total alkalinity.

ALKALINITY: Also called Total Alkalinity. A measure of the pH-buffering capacity of water or the water's resistance to change in pH. It is composed of the hydroxides, carbonates and bicarbonates in the water. When we measure the total alkalinity, we usually only measure the carbonate alkalinity level.

ALUMINUM SULFATE: Also known as Alum. This product is used as a flocculant which attracts suspended particles in the water to each other. Alum sinks everything to the bottom, which can then vacuumed to waste. A small amount of alum can also be used as a sand filter additive.

AMMONIA: (NH3) It is a nitrogen-containing compound introduced into the water by swimmers as waste (perspiration or urine) or by other means. It quickly combines with chlorine to form bad-smelling chloramines, which are harmful to our health.

ANTI-FOAM: A chemical added to the water to reduce the foam. These products do not remove the source of the foaming. Shocking and superchlorination may help prevent foaming. Careful use of cheaper algaecides/ algaestats can prevent foaming.

AUTOMATIC POOL CLEANER: A pool maintenance system that will brush or vacuum dirt and debris from the interior of the pool automatically. Some cleaners work on low-voltage electricity, others on the pump's suction line. The pool cleaner may be programmable, automatic or may move randomly around the pool. Some cleaners can climb the walls of the pool, while others only clean the floor.

AVAILABLE CHLORINE CONTENT: A term used to compare the amount of oxidising power that chorine-containing products have when compared to gas chlorine(Cl2). It permits easy comparison of relative values of chlorine compounds.

AVAILABLE CHLORINE: The amount of free chlorine that is available to sanitise or disinfect the water. It is also called Residual Chlorine and Free Available Chlorine.

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BACKFLOW: The back-pressure of water in a pipe in the opposite direction to normal flow.

BACKWASH: Thoroughly cleaning a sand filter by reversing the flow of water through it so that the dirt and rinse water go to waste.

BACTERIA: Unicellular microorganisms of various forms. Some are pathogens, which can cause infectious diseases. Bacteria are controlled by chlorine, bromine or other sanitisers or disinfectants.

BACTERICIDE: Meaning to kill bacteria. It is a chemical (e.g. chlorine) or an element (e.g. silver) that kills bacteria.

BAKING SODA: Chemically, Sodium Bicarbonate. It is white powder used to raise the total alkalinity of pool water without having much affect on pH. It will only increase pH up to 8.5, regardless of the quantity used. Care should be taken, however, to avoid adding large quantities at one time.

BALANCED WATER: Balanced water is the result when all of your chemical parameters are within the tolerance limits. The most important parameters of water balance are pH, Total Alkalinity, Calcium Hardness and Temperature, as measured using the Langelier Saturation Index .

BASE: Chemicals of alkaline nature which will counteract the pH of an acid. Common bases used around the pool include Soda Ash, Sodium Bicarbonate and Sodium Carbonate. A base is the opposite of an acid. See Alkali

BASE DEMAND: A titration test used to determine the amount of a base (alkali) required to increase the pH to the correct level.

BCDMH: Chemically, "bromochlorodimethylhydantoin", it is a bromine sanitiser. When BCDMH dissolves in water it produces Hypobromous Acid and Hypochlorous Acid.

BICARB: See Sodium Bicarbonate..

BLEACH: This term usually refers to liquid chlorine. It is the same chemical used in the home, but pool chlorine (sodium hypochlorite) has 12% - 15% available chlorine while laundry bleach only has about 5% available chlorine.

BLEACHING OUT: At above 10ppm free available chlorine in a pool, a DPD test kit often indicates zero chlorine because the reagent is being destroyed. If you observe an initial pink colour which then rapidly fades, you probably have far too much residual chlorine in the water.

BIGUANIDES: The name for a certain class of sanitizers using the polymer PHMB, the only non-halogen sanitiser available for pool use. Soft Swim and Baquacil are manufacturers of this sanitiser. Biguanides are NOT compatible with the Pool Wizard.

BLUE FINGERNAILS: A condition caused by too much free copper in the pool water. Can result from cheaper copper-based algaecides, overuse of these algaecides or corrosive water. See also Green Hair.

BOOSTER PUMP: In addition to the filter pump, a booster pump may be necessary to power some automatic pool cleaners.

BREAKPOINT CHLORINATION: When you shock treat your pool, the goal is to reach a high enough level of free chlorine to break apart all molecular bonds; specifically the combined chlorine molecules, ammonia or nitrogen compounds and to completely oxidise all organic matter. Adding enough chlorine to achieve this is breakpoint chlorination. Chlorine added after that point will be free available chlorine.

BROMAMINES: By-products formed when bromine reacts with swimmer waste (perspiration or urine), ammonia or nitrogen. Unlike chloramines, which are strong smelling and have very low sanitising properties, bromamines are active disinfectants and do not smell, although high levels are harmful to your health.

BROMIDE: A common term for a bromide salt which, when added to water becomes hypobromous acid, the active form of bromine. It is used as a disinfectant in swimming pools.

BROMINATOR: A mechanical or electrical device for dispensing bromine at a controlled rate. It is most commonly a cannister or floater filled with bromine tablets.

BROMINE: A member of the halogen family commonly used as a sanitizer or disinfectant to destroy bacteria and algae in swimming pools. It is resistant to heat and rapid pH fluctuations. Available as a tablet or as sodium bromide, a granular salt.

BUFFER: A chemical which results in resistance to changes in pH. A base such as Sodium Bicarbonate, when added to your pool will increase total alkalinity. This in turn increases the buffering capacity of the pool; i.e. your pool's resistance to pH change.

BUFFERING CAPACITY: The ability of the pool to resist changes in pH. The buffering capacity is determined by the total alkalinity. If your pH bounces, or resumes previous levels soon after adjustment, the buffering capacity is too low. If your pH rises rapidly, even after the addition of large amounts of acid, the buffering capacity is too high. If the pool has an unstable pH, the total alkalinity should be tested and adjusted.

BYPASS: An arrangement of pipes, gates and valves by which the flow of water may be passed around the filter rather than through it, and usually refers to circulating the water without filtration.

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