A chemical compound which releases hydrogen ions into water, decreasing pH.

Acid Demand

The amount of acid needed to lower the pH and alkaline levels of pool water to the correct level. Determined by the acid demand test.

Acid Demand Test

A test used with a pH test to determine the amount of acid needed to lower pH and alkaline levels.


The state of being acidic – less than 7.0 on the pH scale.


A thermoplastic sheet that is formed into a mould to make a spa or related equipment.

Aggressive Water

Unbalanced water that attacks and corrodes pool surfaces, fixtures and pipes.

Air Blower

A device that forces air through holes in the floor, bubbler ring or hydrotherapy jets in a spa.

Air Relieve Valve

A manually operated valve at the top of a tank for relieving the pressure inside and removes the air inside.


Microscopic plant-like organisms containing chlorophyll. Their microscopic spores are continually introduced into the pool by wind, rain showers, etc. They grow rapidly in pool water when exposed to sunlight and temperatures above 40 degrees. If not controlled by chemical treatment, they form unpleasant slime and odour. Algae can affect the filtration process and increase the need for chlorine.


A chemical agent specifically designed and used to kill algae and prevent their recurrence.


A condition when the water is above 7.0 on the pH scale.


An aluminium sulphate compound to help clarify water. Alum lowers the pH of the water.


Usually introduced into the water through waste (sweating, urine, etc.). It quickly forms odorous, body-irritating chloramines.


Invisible organisms of various forms, some of which can cause infections or diseases. Bacteria are controlled by chlorine, bromine, or other sanitizing agents.

Balanced Water

Water containing just the right amounts of Calcium Hardness, Total Alkalinity, pH and Dissolved Solids to prevent scale and corrosion.

Ball Valve

Used to regulate the flow of water and to shut off skimmers, drains and other lines to vacuum or run a spa or other water feature.

Base Demand

The required amount of pH increasers to increase the pH level of pool water to the ideal range of 7.2 to 7.6.


An electrical device that produces a continuous rush of air to create the optimal bubbling effect in a spa, hot tub, or whirlpool.

Blue Fingernails

A condition caused by too much copper in the pool water. Blue fingernails are not caused by chlorine. The copper causes pH levels to lower and dissolve the metal components of the equipment. The dissolved metal then stains hair, fingernails, and pool walls. It can also be caused by keeping the pH too low or misusing acid.


An elemental mineral used for conditioning water to provide clearer, more comfortable water.

Bottom Circulation System (BCS)

Also called the main drain. It is a separate system that is installed beneath the pool connecting to the filter. The system circulates the water from below.

Breakpoint Chlorination

The process of adding sufficient chlorine to completely oxidize all organic matter, ammonia, or nitrogen compounds. All chlorine added after that point is free available chlorine.


A sanitiser commonly used in spas. Effective against bacteria but cannot be stabilized, so it is susceptible to deterioration by sunlight. Unlike chlorine, it can be combined with ammonia compounds and still be an effective sanitiser.


Chemicals that serve to prevent fluctuations in pH.


Pipes, gates, and valves by which the flow of water may be passed around equipment or diverted to another piece of equipment, creating a diversion.

Calcium Carbonate

Scale that forms from calcium compounds when pool water is too alkaline, calcium hardness is too high or total alkalinity is too high. These hard deposits accumulate on pool surfaces and equipment.

Calcium Chloride

Also called "Calcium Up" it is a soluble white salt used to raise the calcium hardness of the pool water when required.

Calcium Hardness

A measure of the level of calcium and magnesium in water. Helps to determine how scaling or corrosive the water is.

Cartridge Filter

Filter with a pleated element that traps debris. Looks like a giant oil filter.

Check Valve

A mechanical device in a pipe that permits the flow of water or air in one direction only.

Chelating Agent

A chemical that binds up metals to prevent metal staining and coloured water.

Chemical Feeder

Any of several types of devices that dispense chemicals into the pool or spa water at a predetermined rate.


Compounds formed by combining with nitrogen compounds from human waste such as perspiration, urine, and skin proteins. Chloramines have an objectionable odour of "too much chlorine" and can irritate swimmers' eyes and skin.


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


The most widely used bacteria-killing agent for recreational water treatment. A sanitizer and an oxidizer.

Chlorine Demand

The amount of chlorine required to control bacteria, algae, and other contaminants in swimming pool water.

Chlorine Neutralizer

A chemical used to make chlorine harmless.

Chlorine Residual

The amount of chlorine that remains in the water after the chlorine demand has been met.


The flow of water in a swimming pool or spa.


A chemical compound added to water to gather particles together for filtration.


An element often found in various pieces of spa equipment. Corrosive water caused by misuse of chemicals or improper water balance can cause copper to be dissolved from the equipment or plumbing. Copper is also used as an algaecide.


The state of deterioration of the pool or spa or equipment. Caused by improper water balance, and misuse of acid or acidic products.

Corrosive Water

A water condition of low pH that can corrode metal pipes, pumps and fixtures.

Cover, Hard Top

A cover used on pools, spas and hot tubs that rests on the lip (coping) of the pool or spa deck.

Cover, Solar

A cover that, increases the water temperature by absorption and harnessing solar power and reduces evaporation.


Presence of unusual colours in the water.


Break down oily substances and convert them to water and carbon dioxide.


A device that is used to filter fine debris out of pool water.

Filtration Rate

The rate at which the water is traveling through the filter.

Flow Rate

The quantity of water flowing past a point within a specified time.


A froth of bubbles on the surface of water. Usually comes from soap, oil, deodorant, hair spray, etc.


Cloudiness in the water caused by small particles.


Device used to heat the water of a pool, spa or hot tub.

Main Drain

The part of the pool that provides water circulation. Water can be removed from the pool through the main drain.


A chemical used to make chlorine or bromine harmless.


A gas that causes algae to bloom and disables chlorine. An element that when combined with chlorine forms chloramines.

pH (potential Hydrogen)

A measure from 1-14 of how acidic or basic the water is. A pH of 7.0 is neutral. Pool water should be kept slightly basic with a pH of 7.2-7.8.


A motor-powered mechanical device that creates pressure and water flow to provide circulation through the filter and heater.


A general term for a substance used as a disinfectant to kill bacteria and algae and oxidize organic contaminants.


Mineral deposits that form on pool or spa surfaces and equipment due to excessive calcium in the water when the pH level is high.


Matter that rises to the surface of the water and forms a layer or a film.

Shock Treat

The practice of adding a significant amount of an oxidizing chemical to the water to control ammonia, nitrogen compounds or waste.

Sodium Thiosulfate

A chemical used to neutralize or de-chlorinate pool and spa water.

Soft Water

Water low in calcium and magnesium mineral content (water hardness) - usually less than 100 ppm. Pools and spas should not be filled with soft water from a softener.

Source Water

It is the water used to fill or refill the pool or spa.

Test Strips

Chemically treated strips. Dip them into the water and read the reactions. These strips can test free available and total chlorine, bromine, pH, calcium hardness, total alkalinity and cyanuric acid.

Titration Test

A test used for acid and base demands, total alkalinity, and calcium hardness


Any number of devices that use suction to collect dirt and debris from the bottom and sides of a pool or spa.

Vinyl Liner

The vinyl liner is the product that covers the walls and base of the pool and holds in the water. The vinyl liner is durable and easy to clean.

Water Balance

This balance is reached when all elements (pH, total alkalinity, calcium hardness, total dissolved solids and temperature) are within their proper ranges.