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Chemical Glossary

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Alkaline refers to the condition where the water's pH is above 7.0 (neutral) on the pH scale. It is the opposite of acidic. Alkalinity is the amount of carbonates and bicarbonates in the water, measured in ppm of Total Alkalinity.



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, polyquat compounds, chlorine enhancers , and herbicides.


Algae may form on your pool surfaces or it may bloom in suspension. We typically know algae to be green, but it may also be yellow (mustard algae), black, blue-green or any shade in between. It may form separate spots, or seem to grow in sheets. Pink algae is not algae at all, but a form of bacteria. Algae are living, breathing organisms that need warmth, sunlight and CO2 to thrive.


Liquid (Muriatic Acid) or dry granular (Sodium Hydrogen Sulphate) substance used to lower the pool's pH (toward a more acidic condition) or to lower total alkalinity levels.


A base such as Sodium Bicarbonate (Baking Soda) added to your pool will increase alkalinity which increases the buffering capacity of the pool or your pool's resistance to pH change.


A member of the halogen family, commonly used as a sanitiser in spas, because of its resistance to hot water with rapid pH fluctuations.


A combined bromine - ammonia molecule. Unlike chloramines which are strong smelling and offer no sanitizing properties, bromamine compounds continue to sanitize.

Break Point Chlorination

When you shock your pool the goal is to reach a high enough level of free chlorine (measured in ppm) to break apart molecular bonds, specifically the combined chlorine molecules. When break point is reached with sufficient additions of chlorine, everything in the pool is oxidized.

Balanced Water

Balanced water is the result when all of your chemical parameters are where they should be, and thus "balance" each other. The key components of water balance are pH, Total Alkalinity, Calcium Hardness and Temperature.


From a health perspective, the most dangerous micro-organisms which may be living in the pool water. Some are pathogens, which can cause infectious diseases.

Chelating Agent

A chemical which binds metals. Used to prevent metal staining and water discolourartion.


Calcium Hypochlorite

A popular chlorine sanitiser in granular form. Calcium Hypochlorite has a long shelf life & is commonly used to shock the pool.

Cyanuric Acid

Also Known as a conditioner or stabaliser. A granular chemical added to the pool water which provides a shield to chlorine for protection from UV radiation which disrupts the chlorine molecule, destroying its sanitising ability. Important in salt chlorinator pools as the chlorine generated by these is not stabalised.


The effects of an acidic pool environment, one in which the pH and/or alkalinity are very low. Corrosion in the form of etching, pitting or erosion of pool equipment and surfaces is the result.


An effective algaestat and algaecide. Copper is used in many pools products e.g. Long Life Algaecide.


Any micro-particle or organism which reduces water clarity, quality or presents health hazards.


The properties of a chemical used in the assemblage and precipitation of suspended material which may make the pool appear cloudy.


A clarifier is a chemical used as a coagulant of suspended micro-particles. It aids Filtration by clumping smaller particles together to allow them to caught in the filter.

Chlorine demand

Is the difference between the amount of free available chlorine or combined available chlorine compared to the amount of chlorine added to a water system at the end of a specific time period.

Combined Chlorine

That portion of total available chlorine left over when free chlorine is subtracted. The measure of chlorine which has already attached itself to other molecules or organisms. Most of this is made up of chloramines.


A member of the halogen family of sanitisers. It's use in swimming pools is in the elemental form of a gas, liquid, granular or tablet compound. When added to water it acts as an oxidizer, sanitiser, disinfectant and all around biocidal agent.


A chlorine-ammonia molecule which is an undesirable, foul smelling, space taking, compound that require shocking the pool water to get rid of.

Dry Acid

Sodium Bisulfate. A granular form of acid used to lower pH and alkalinity in the water. Safer and less caustic than muriatic acid. Also Known as pH Minus or pH Reducer.


A method of testing chlorine levels in pool water. Unlike OTO, DPD testing allows determination of total and free available chlorine levels. When free is subtracted from total we get combined levels.


Chemicals or processes which work to destroy vegetative forms of microorganisms and other contaminants. Examples are chlorine, bromine, Soft-Swim, ionizers and copper and silver algaecides.


Used in swimming pool formulations designed to break down and digest oils in a pool or spa similar to the way enzymes are used in oil spill clean-up efforts.


A term used to describe surface foam on your water especially in spas/hot tubs. Foaming is caused by high TDS levels working in combination with soft water and oils. Certain low grade algaecides can foam when added to pool or spa. Use enzymes for foam control.



Essentially the same as a coagulant. This chemical (such as aluminium Sulphate) is used to combine suspended alkaline material and/or algae into a heavy gel which sinks to the bottom for vacuuming.

Fill Water

Used in filling or adding to the water level. Whether from a hose or from a well, your fill water brings its own chemical make up and water balance (or lack thereof).

Free Chlorine

Free, available chlorine is that which is active, not combined with an ammonia or a nitrogen molecule, and ready to react to destroy organic material.

Hydrogen Peroxide

A non-chlorine oxidiser (shock) used with biguanide systems.


A family of chlorine compounds. Granular Calcium Hypochlorite and Lithium Hypochlorite and the liquid Sodium Hypochlorite. When these compounds contact water they release the active sanitizing agent Hypochlorous Acid

Hard Water

Water which is high in calcium hardness and other salts which can cause scaling. A characteristic of hard water is soap resists being lathered.


A group of elements on the periodic table used mainly as sanatisers. Contains fluorine, bromine, chlorine, iodine & astatine.


An Ioniser is a device mounted on your return line, through which water flowing will receive charged metal ions. Manufacturers may use a copper anode and/or silver. Copper is an algaecide and algaestat, while silver is known for its properties as a bactericide.


Usually introduced into the water from iron plumbing or from well water. Ferric Iron can stain surfaces while Ferrous Iron will turn your water a clear green color.


Such as Calcium, Manganese, Magnesium, Nickel, Copper, Silver, Iron, Cobalt or Aluminum. Their presence in high non-chelated concentrations can lead to stains & scale when conditions are right.

Non-Chlorine Shock

A granular form of potassium permonosulfate, used to oxidize materials such as microorganisms, contaminants or chloramines.


When combined with chlorine, nitrogen creates chloramines, which do not belong in a pool. Nitrogen can be found in many swimmer wastes (perspiration, suntan oil, hair tonics, etc.) or can be introduced by other means.


A device used to generate ozone. Assists in disinfection, deodorising and flocculating.


Chemical that burns up organic matter.


The molecule containing three atoms of oxygen known to be a very powerful sanitiser. Ozone producing equipment creates this molecule by UV radiation or corona discharge generators.


The "burning up" of organic waste and compounds in the pool water. It also refers to what you may see on your metal pool surfaces if your water is corrosive. Rust is a form of this kind of oxidation.


To precipitate is to come out of solution/become insoluble by result of chemical action. Material forced out of solution purposefully or accidentally will then settle, stain, scale or remain suspended in the water.


Parts per million. A method of assigning value to certain concentrations of chemicals in the water. One part per million (ppm) denotes one part per 1,000,000 parts. This is equivalent to one drop of water in 50 litres.

Potassium Perminisulphate

See Non-Chlorine Shock


The scale of relative acidity or alkalinity expressed in logarithmic numbers on a scale from 0 - 14, 7.0 being a neutral pH. What's really being measured is the hydrogen ion concentration. Some would say pH stands for Power of Hydrogen.

Quaternary Ammonium Compound

A type of algaecide composed of ammonia compounds. An effective algaestat for green and blue/green algae.


Usually refers to free available chlorine levels remaining in the pool after initial treatment or activity with contaminants.


The chemical indicators used in testing water balance. Usually in liquid or tablet form.

Sequestering Agent

A chemical which bonds with metals to deter staining or discoloration (see Chelating Agent).

Swimming Pool Test Strips

Litmus paper strips that you dip into the pool water. Once taken out of the water they change colour; this colour matches up to a chart with numerical values on it.

Swimming Pool Test Kit

Used to test the water for pH/chlorine/bromine/TA etc. Available in many forms from easy to read test strips to 25 test digital meters.


Applying 7 - 10 times the normal amounts of chlorine to the pool as an added boost for contaminant removal. Some refer to super-chlorinating as being less than shocking in that break-point thresholds are not reached.


See Cyanuric Acid

Soft Water

Water that has low calcium and/or magnesium content. Characteristically Soap lathers easily in soft water.

Sodium Tetraborate

A chemical that renders algae incapable of processing carbon dioxide. Unable to process Carbon Dioxide the algae will die.

Sodium Hypochlorite

Liquid chlorine used in pools.

Sodium Dichlor

A granular form of chlorine that is stabilized with cyanuric acid. Used for shocking and super-chlorination.

Sodium Bisulphate

See Dry Acid.

Sodium Bicarbonate

Also known as TA Plus. Increases alkalinity more than pH. Used to raise Total Alkalinity levels

Soda Ash

Also known as pH Plus. Used to counteract an acidic condition by raising pH.

Total Dissolved Solids (TDS)

A measure of everything that has ever dissolved in the water; all the matter that is in solution. High TDS levels can over-saturate your water causing all sorts of reactions.

Total Alkalinity (TA)

The ability of the pool water to resist changes in pH; the 'buffering' capacity of the water. Additions of Sodium Bicarbonate will increase the levels. Expressed in ppm.

Total Chlorine

The sum of combined and free chlorine levels.

Ultra Violet Light Treatment (UV)

Using UV wavelength radiation to destroy contaminants in water. UV light is also used to create ozone molecules for the same purpose.

Pool Glossary

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Air Leaks

Results when connections on the pumps suction side are not air tight. Pumps need to create a vacuum to work properly. Air leaks can cause high pressures which can damage the pump, filter or both. Aerated water can cause foam.

Automatic Pool Cleaner

A device which automatically vacuums debris from the walls and floor of the pool (depending on model). A great labour saving product, available in suction, booster & electric models.

Automatic Safety Cover

Solid, reinforced vinyl which rolls onto a reel on one end of the pool and attaches to the pool sides in a small aluminum track. Some models may snap the sides into small anchors placed into the deck, providing more shape flexibility. Can be motorized or hand crank. Provides safety (with water pumped off), debris protection and heat/chemical/water retention.

Air Dome

Made of PVC. When inflated acts as an enclosure for a swimming pool. An air dome can be removed and can extend your swimming time in the cooler months. Can also be used for other things, such as tennis courts.

Air Bleeder Assembly

Located on the top of the filter sometimes accompanied by a pressure gauge. The bleeder is opened to release air trapped in the filter.


British Thermal Unit. A unit of measurement for the use of gas by a gas appliance. Pool heaters are rated by their consumption.

Booster Pump

Secondary to the filter pump, a booster pump is used to power an automatic pool cleaner such as Polaris.


Plumbed into the spa return line, air is injected to produce bubbles and a hydrotherapy effect in the spa.

Ball Valve

A plumbing part with a hollowed out ball inside which can be turned with an external handle to decrease or increase water flow.

Backwash Hose

The backwash hose is used in the backwashing system, it connects to the filtration system and when you switch to backwash the water then runs out through this hose out to a drain.


The process of thoroughly cleaning the filter medium and/or elements by reversing the flow of water through the filter to waste.


The re positioning of the soil after construction of a pool back behind the walls.

Calcium Hardness

A measure of the level of calcium salts in the water. Helps to determine how scaling or corrosive the water is. It is especially important to monitor calcium hardness for possible build-up on heater elements.

Counter Current Unit

Situated in your pool wall or hanging over the edge; a counter current unit generates a current in the water to swim against rather than swimming lengths up and down the pool. Especially useful in a small pool where length swimming is not possible but the exercise benefits are required.


A plumbing fitting designed to join two pieces of pipe. Also known as a plain socket or straight connector.

Corner Step Unit

Situated in the corner of the pool (ideally the shallow end) made of fibreglass and normally consisting of 4 steps, these allow easy access in and out of the pool.

Coping Stone

The capstone on top of the bond beam which finishes the edge around a pool or spa. It may be precast concrete or natural stone. On vinyl liner pools coping is usually part of an integrated system for the wall, vinyl liner and deck.


A pipe, usually grey PVC or flexible PVC designed to carry wires from a source (e.g. time clock) to a load (e.g pump).

Circulation System

The 'circuit' of plumbing which continuously carries the water out of the pool, through the pump & filter and returns it to the pool.

Circuit Breaker

A switch which allows manual override of an electrical circuit. Also automatically breaks the circuit when current fluctuations are detected.

Chlorine Generator

Creates its own sanitiser for your pool, usually from salt added to the water.


Device which allow for the safe, controlled introduction of chlorine into the water.

Chemical Feeder

Dispenses sanatising chemicals into your pool. available as inline or offline versions allows semi-automatic sanatising.

Check Valve/Non Return Valve

Plumbing fitting designed to prevent water from returning back along the pipeline. Commonly used when a chemical feeder is present to prevent super chlorinated water from the feeder working its way back to delicate heater elements and exchangers.

Drain / Vacuum to Waste

A useful setting on a Multi Port Valve allows you to vacuum up large volumes of debris that would either clog the filter or pass through it because of its small size. Dirt that is vacuumed bypasses the filter media right out the waste line. It is also the setting of choice when draining the pool or lowering the water level.


Can also be called main drain or sump; this plumbing fitting is the start of one suction line to the pump and is usually situated at or near the center of the bottom of the pool.

Diverter Valve

Used in a twin port skimmer a diverter valve allows the operator to manipulate the amount of flow from the main drain and skimmer to the pump.

Diatomceous Earth

The filter media of the DE filter. This dry powder is the fossilized remains of the ancient plankton diatom.

Deck Box

Small poolside fitting which houses a connection from the light back to the transformer in the plant room.

Equal Tee

A plumbing fitting used to bring two pipes together into one or vice-versa.


A 90 or 45 degree plumbing fitting. Used where pipes need to take a turn.


The water that flows out of the pump on its way through the filter, heating and treating equipment then returning to the pool. Also known as the pressure side.

Flow Rate

Quantity of water flowing past a designated point within a specified time period; measured in gallons per minute (GPM) or metres cubed an hour (m3/hr).

Filtration Rate

The rate of water pumped through a filter. Measured in gallons per minute (gpm) or metres cubed an hour (m3/hr).

Filter Pump

The device that pulls water from the pool and pushes it through the filter and on its way back to the pool.

Filter Media

A finely graded material such as sand, glass, diatomaceous earth or polyester fabric that removes suspended particles from water passing through it.


Used to remove particles suspended in the water by pumping water through a porous substance or material. Also the setting on a Multi Port Valve to allow normal water flow through the filter.

Fibre Optic Lighting

Fibre optic lighting transforms any pool and gives you the freedom to light pools, spas, water features and surrounding landscapes in exciting and dramatic colours.


A dry mixture of cement and sand mixed with water at the 'gun' hence the name. A gunite operator shoots the pool's rough shape, while finishers trowel after.


A Ground-Fault-Circuit-Interrupter (GFCI) device protects a circuit from branching off by de-energizing the path of electricity very quickly when it senses current loss. An important safety device around water.

Gate Valve

Used to shut of the pipe to stop water flowing through. Used commonly in spa's either side of the heater/control panel to allow removal of it if needed whilst keeping the water in the spa.

Gas Valve

An electronic valve in the pool heater that directs gas flow from the meter to the pilot and the burner tray.

Hydrostatic Pressure

A force involving built up ground water which creates upward pressure beneath the pool shell.


This is a finished edge which is an option on covers. Sewn onto the perimeter of the cover it improves the life expectancy as it protects the cover from wear and tear at the edges.


A device used to heat the water. It may be electric, fuel operated or solar powered heat.

Heat Pump

Similar to an air conditioner but in reverse. The heat pump's cooling coil removes heat from the air while the condenser coil transfers it to water cycling through it.

Heat Exchanger

Allows the heating of pool water from an external boiler not connected to the pool water flow. A series of tubes inside a larger tube. the small tubes inside have the pool water flowing through while the heated water from the boiler passes over them in the larger tube. the heat from the boiler water is transferred through these tubes into the pool water. Also available in plate form where a plate.

Hard Cover

A cover which rests on the edge or coping of the spa or small pool. Provides a barrier to debris and possibly people, whilst keeping the heat trapped in.


This returns water from the filtration system back into the swimming pool.


The water coming into and up to the impeller from the suction lines. These pipes are under vacuum pressure.


The rotating vanes of a centrifugal pump; its action creates the flow of water. The impeller is shaft driven by an electric motor.

Jet Pump

Used in spas to provide additional thrust into the hydrotherapy jets.

Low Water Suction

An influent fitting, typically low on the wall in the deep end of a pool. A cheaper alternative to a main drain.


An electric device which consumes energy, placing a load on the source.


The most popular and cost effective way of pool finishing. Manufactured from vinyl and can come in many different thicknesses, patterns and even textured. can be made to fit into your pool or lined on site.

LED Underwater Light

LED underwater lights are another way of underwater lighting. With an average life expectancy of 100,000 hours with a maximum power consumption of only 25W for the coloured and around 10W for the white.


Elongated, capped plastic nipples at the bottom of a sand filter which are slotted to allow for water passage while keeping the media in the filter tank.

Ladder Bumpers

Rubber caps or inserts which protect the pool plaster or vinyl liner from the sharp steel ends of the ladder.

Multiport Valve

A 4 or 6 position valve combining the functionality of several valves into one unit, revolutionizing pool plumbing.


A machine for converting electrical energy into mechanical energy. Your motor is known as the dry end of the filter pump. It drives the impeller, which moves the water.

Mechanical Seal

A seal behind the impeller which prevents water from running out along the shaft of a motor. Also called a pump seal.

Main Drain

See drain.

Overflow Grating

Overflow grating is used on deck level pools (a pools filled to the top with water). The water overflows into a channel covered by overflow grating


Starting a flow of water to a pump so it wont suck air.


Polyvinyl chloride. Used in many applications in the pool industry for example flexible and rigid PVC pipe.


A mechanical wet-end powered by an electric motor. Creates hydraulic flow and pressure for the circulation of the pool water.

Pressure Switch

A switch used in pool heaters which activates when the flow rate is insufficient for safe heater operation. This disrupts the circuit in the heater, preventing it from firing.

Pressure Side

The return side of the plumbing. The section from the pump impeller towards the pool.

Pressure Gauge

Indicates pressure in a filter system. Provides a determination of how the system is operating. On a sand filter informs when a backwash is required.

Pressure Check

A test for the rate of water flow. Also a test for leaks in plumbing by placing a line in question under pressure and waiting for the pressure to drop.

Plaster / Screed

A common type of interior finish applied over the concrete shell of an in-ground swimming pool.

Roman End Step Unit

These differ from corner step units as they sit on the end or side wall of a pool rather than tucked in the corner. Manufactured from fibreglass, usually half moon shape and mainly consisting of 4 steps. There is also the option to have an internal roman end step unit where the steps stick into the pool.

Roller / Reel

This is a device which allows the swimming pool cover to roll on and off the pool with ease. There are many different models to choose from depending on the cover size and the cover material.


After back-washing its important to rinse for 15-20 seconds to remove any residual dirt that may work its way back into your pool after back-washing. The rinse setting pushes the water the same way as the filter setting but effluent is sent out the waste line.

Restricted Flow

The term used to describe a condition preventing full flow of water. Restriction can occur from many things i.e. full skimmer or strainer baskets, obstructions in the plumbing, dirty filter media, undersized plumbing or equipment or placing devices such as heaters in the circulation system. Restriction on the suction side creates a higher vacuum (or suction) while on the return side creates higher pressure.


This Multi Port Valve setting bypasses the filter. Water coming into the multi port completely avoids the filter media and heads back towards the pool. Used only when the filter is broken( to keep pool water circulating and not becoming stagnant), or when adding specialty chemicals which specify using this setting.


Reinforcement bar. Made of Steel and used to add strength to a concrete pool. After excavation of an in ground pool a steel cage is formed out of re-bar. The gunite (concrete mix) shell is shot over and surrounding it.


The amount of time it takes the pump to move all the water in the pool through the filter and back again. The required domestic rate is between 4-8 hours.

Top Mount Sand Filter

A top mount sand filter simply means that the multi port valve is connected via the top of the filter rather than the side on a side mount.

Time Clock

A mechanical device that controls the timed operation of your electrical equipment, primarily your filter and booster pumps.


This enables you to set control control the temperature for any water system.

Under water Light Niche

The part of the pool light that is cast into the wall. Houses the guts.

Underwater Light Guts

The guts are the part that sit inside the niche. they contain the bulb, the bulb connection and a coil of wire to allow it to be floated to the surface to change the bulb.


The lower collection system in a filter which directs filtered water back towards the pool. It also distributes water in reverse during back-washing. See laterals.

Vinyl Liner

One type of interior finish. The liner is draped over a sand or cement floor, and locked into the top of the wall.


Increasing water velocity by restricting pipe size.


A device placed in the plumbing line which restricts or obstructs water flow to create desired hydraulics or permit flow in one direction only (check/non return valve).

Vacuum Point

An inlet fitting in the wall of your pool usually close to the water line. Allows a suction pool cleaner or vac hose to be attached for cleaning.


Refers to the low pressure condition created in the suction line. Also refers to the cleaning process of sucking leaves, algae and debris from the pool floor.

Winter Cover

A barrier to sun and debris, winter covers secure the pool from contamination.


Either flap or collar. The weir floats at the surface meaning that floating debris is drawn towards it and sucked down into the skimmer basket.

Spa Glossary

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Air Lock

Results when air bubbles form in the plumbing, usually during draining and refilling.

Air Leaks

Results when connections on the pumps suction side are not air tight. Pumps need to create a vacuum to work properly. Air leaks can cause high pressures which can damage the pump, filter or both. Aerated water can cause foam.


A durable and nonporous material used to form the hot tub surface.


Aromatic and attractive wood sometimes used to finish the hot tub exterior cabinet.

Calcium Hardness

A measure of the level of calcium salts in the water. Helps to determine how scaling or corrosive the water is. It is especially important to monitor calcium hardness for possible build-up on heater elements.

Digital Programming

Popular controls used to manage features such as water temperature, filtering cycles, light and accessories such as stereo and TV.


A chemical which reduces and/or eliminates foaming.

Flow Monitor

Gauges how fast and how much water is flowing.

Filter Cycle

A programmed period of time that the hot tub filters water each day. Also can refer to the length of time between cleaning or replacing the filter element.


A material laid up and/or shaped to form hot tub shells.


Makes chlorine from dissolved salt water, in the hot tub, as it is pumped through an electronic cell and back into the water.


In excess is associated with mildew, especially on indoor hot tubs where moisture tends to be trapped in the hot tub room.


A device that generates copper, zinc and silver ions to kill bacteria and algae.


Grated openings in the hot tub shell plumbed to the filter through which water is pulled by the pump(s). Hot tubs without intakes draw water through the skimmer at the surface into the filter system. No pump should be attached to just one suction fitting.


A polymer-based, foam-like material placed between the hot tub shell and the air around the shell. Helps to prevent against heat loss, muffles sounds of pump operation, conserves energy and can strengthen the shell.


The openings through which water flows into the hot tub. There are many different types of jets to give a different massage experience.

Lighting Spa

Can be arranged around the perimeter, underwater and other various ways to create atmosphere in a hot tub.


A process in which materials with differing properties are layered and bonded to each other to achieve greater strength, lower heat transfer and better sound absorption.

Organic Matter

Debris such as microorganisms, pollen etc, that need to be burned up or oxidised regularly to prevent haze or algae and chloramines.

Primary Sanitizer

The essential chemical that kills the negative stuff in hot tubs, i.e. bromine, chlorine and biguanide.


A plastic used to make some hot tub cabinets.


A basket in some spa pumps that collects debris which could restrict water flow.

Stainless Steel

A material which resists staining from minerals. Most grades are impervious to rusting and is used in many heaters. 316-grade stainless steel is best.

Urethane Foam

An insulating plastic used in some hot tubs to protect against heat loss and reinforce the surface to provide support.