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Glossary of Terms

Water Terminology for Your Reference

In this glossary, you will find the definitions for commonly encountered water terminology to help you better understand water testing and basic water chemistry principles.

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Chemical compound with a pH less than 7 and the ability, when in solution, to react with a base to form a salt and to turn litmus red. Also, a substance that releases hydrogen ions (H+) in water. In pool water maintenance muriatic acid and sodium bisulfate, also an acid, are used to lower pH and alkalinity. The opposite of a Base.

Acid Demand
A measure of the amount of acid required to reduce pH to a predetermined level. This can be accomplished using an acid titration procedure, referred to as an Acid Demand Test.

Plantlike organisms that will rapidly proliferate in water absent adequate sanitizer.

Algae Bloom
A rapid increase in the population of algae. Turns pool/spa water cloudy.

Algae Shock
Application of a large dosage of chlorine all at once to destroy built-up chloramines and scour the pool of oxidizable organic contaminants, including a green algae bloom. Typically, the chlorine level would be raised to 30 ppm and then allowed to fall back gradually to below 4 ppm before swimming resumes.

A chemical used to kill algae.

A chemical used to inhibit the growth of algae.


Parameter that is the subject of the water analysis, such as pH or free chlorine. 


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Potentially disease-causing organisms. Proper sanitation eliminates bacteria in pool/spa water.

Balanced Water
Pool/spa water that is neither corrosive nor scale forming. Commonly determined by using the Saturation Index (SI) where perfectly balanced water equals zero.

Chemical compound with a pH greater than 7 and the ability, when in solution, to react with an acid to form a salt and turn litmus blue. Also, a substance that releases hydroxyl ions (OH-) in water. Soda ash (sodium carbonate, 100%) or sodium bicarbonate, 100%, are bases commonly used to raise pH in pool/spa water. The opposite of an Acid.

Base Demand
Amount of alkali material required to raise pH to an acceptable level. This can be determined by performing a base titration, referred to as a Base Demand Test.

A chemical additive to pool/spa water that stabilizes pH, helps prevent algae growth, and prevents scaling in salt water generator cells.

Breakpoint Chlorination
Dosing water with sufficient chlorine to remove combined chorine (chloramines). Dosage is calculated as 10 times the combined chlorine reading.

By-products formed when bromine reacts with contaminants in pool and spa water. Unlike chloramines (combined chlorine), bromamines are effective sanitizers and do not need to be eliminated.

A chemical used to kill microorganisms and oxidize organic material in pool/spa water.

Buffer Solution
An aqueous solution that resists pH change when an acid or base is added.

A long, graduated glass tube of small diameter with a stopcock used to deliver a titrant solution during a titration.


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Calcium Hardness (CH)
A measure of the calcium salts dissolved in water. The main component of scale.

Odorous chemical compounds formed when free chlorine combines with nitrogen-containing contaminates in the water. They have very little sanitizing ability. Also referred to as combined chlorine.

A chemical used to kill microorganisms and oxidize wastes in pool/spa water.

Chlorine Demand
Amount of free chlorine consumed by contaminants in the water.

Chlorine Residual
Chlorine available for sanitation/oxidation after the chlorine demand has been met.

An electronic device that measures the amount of light passing through a test sample which has reacted with test reagents for a specific analyte. This measurement is then used to determine the concentration of the analyte in the sample.

Colorimetric Test
Test method where reagents react with a specific analyte to produce a color proportional to the concentration of the analyte.

Combined Chlorine (CC)


An eating away of a material caused by chemical reactions.

Cyanuric Acid (CYA)
Chemical used to prevent the degradation of chlorine by ultraviolet (UV) light. Also referred to as conditioner or stabilizer.


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Common abbreviation for N,N-diethyl-p-phenylenediamine, a reagent used to determine both free chlorine and total chlorine levels. Will also detect total bromine level. Preferable method for testing sanitizer levels in pool and spa water; usually mandated for use at public facilities by health authorities. Turns the sample water pink when chlorine, bromine, or iodine is present.

Dropper Bottle
Plastic bottle designed with a specially sized hole in the tip for dispensing the exact amount of reagent.


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Free Chlorine (FC)
The form of chlorine available to sanitize and oxidize water. Also referred to as free available chlorine.


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An element found in Group 17 of the Periodic Table. Chlorine, bromine, and iodine are halogens that are often used to disinfect water.

Hardness (Hard Water)
Amount of dissolved minerals, chiefly calcium and magnesium compounds found in water, and expressed as calcium carbonate (CaCO3). May be measured as total hardness (TH) or calcium hardness (CH). Only the CH portion is of concern in pool/spa water as an excess of CH may cause cloudiness and/or scale formation.


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Long Viewpath™ Comparator
A variation of the Taylor Slide™ comparator that employs a longer test cell to increase test sensitivity.


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Magnesium Hardness
A measure of the magnesium salts dissolved in water. It is not used in calculating the Saturation Index.

Midget™ Comparator
A comparator manufactured by Taylor that is used for color-matching tests. Contains eight liquid-color standards.

Muriatic Acid
Chemical compound used to lower pH and total alkalinity. It is also used to help remove stains and scale and to "acid wash" certain surfaces.


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Non-Chlorine Oxidizer
A chemical used to "burn up" contaminants in water. Its chemical name is "potassium peroxysulfate." It does not remove combined chlorine, but it will prevent the formation of new combined chlorine. Use of a non-chlorine oxidizer will allow swimmers to reenter the water sooner. Also referred to as monopersulfate. 

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Common abbreviation for orthotolidine. A reagent used to determine total chlorine or total bromine. OT cannot distinguish between free available chlorine and combined chlorine. Turns the sample water yellow.

A compound (e.g., chlorine, bromine, potassium peroxymonosulfate) used to "burn up" organic contaminants in water.


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A measure of the acidity/basicity of an aqueous solution. The pH scale runs from 0 to 14 with 7 being the neutral midpoint. A pH less than 7 is on the acid side of the scale; a pH greater than 7 is on the basic (alkaline) side of the scale.

Phenol Red
Chemical indicator used for testing pH in the range of 6.8–8.4.

Potassium Peroxymonopersulfate
A non-chlorine oxidizer that "burns up" (oxidizes) contaminants in pool/spa water, freeing up the sanitizer to kill germs. Does not remove combined chlorine but prevents formation of new combined chlorine.

Abbreviation for parts per million.


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To kill all living organisms, including algae, harmful bacteria, and other pathogens.

Saturation Index (SI)/Langelier Saturation Index (LSI)
A numerical value derived from a formula that considers the interrelationships between calcium hardness, total alkalinity, pH, total dissolved solids, and temperature. Used to determine the scaling or corrosive tendency of water. A Saturation Index of zero indicates the water is balanced. To avoid number crunching, this value can be determined with the aid of Taylor's Watergram® Water Balance Calculator.

A buildup of crusty mineral deposits, principally composed of calcium carbonate (CaCO3), that is caused by high calcium hardness, high total alkalinity, high pH, or a combination of these parameters. Scaling water in piping will gradually reduce circulation and inhibit heat transfer.

The periodic addition of chlorine to help remove the buildup of organic contaminants such as body oils, perspiration, personal care products, dust and dirt, etc., in pool or spa water. Chlorine compounds (e.g., calcium hypochorite) used as a shock will oxidize contaminants and leave a sanitizing residual behind, whereas a non-chlorine product (e.g., potassium peroxymonosulfate) can only oxidize, so a supplemental sanitizer must be added. Use of a non-chlorine oxidizer will allow swimmers to reenter the water sooner.

Slide™ Comparator
A comparator manufactured by Taylor that is used for color-matching tests. Contains nine liquid-color standards. Used to compensate for color and/or turbidity in the water sample.

Soda Ash (Sodium Carbonate)
Chemical used to raise pH levels. Causes a slight increase in total alkalinity.

Sodium Bicarbonate (Baking Soda)
Chemical used to raise total alkalinity levels. Causes a slight increase in pH.

Sodium Bisulfate
Chemical used to lower pH and total alkalinity; Also referred to as dry acid.

Soft Water
Water lacking the ions which form scale. Pool or spa water entirely lacking hardness will aggressively seek calcium from contact surfaces.



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A method of testing where a reagent of known strength (titrant) is added to a water sample containing an indicator until a specific color change indicates the endpoint of the reaction. The volume added, recorded by drops or milliliters, is multiplied by a factor relating to the titrant to determine the concentration of the analyte tested.

Total Alkalinity (TA)
A measure of the acid-neutralizing capacity of water which indicates its buffering ability, i.e., resistance to changes in pH. Generally, the higher the total alkalinity, the greater the resistance to pH change.

Total Chlorine (TC)
The mathematical sum of free chlorine and combined chlorine.

Total Dissolved Solids (TDS)
The measure of all solids dissolved in a sample of water.


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Water Quality
A measure of water's suitability for a specific application. The intended use determines what characteristics are desirable in the water chemistry.

Water Treatment Program
A plan for managing water quality by mechanical and/or chemical means.

Watergram® Water Balance Calculator
Taylor device used to determine the Saturation Index.


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