Glossary of Pool Terms

This is a comprehensive glossary of commonly used swimming pool and pool cleaning terms. While not every regional term or brand name is included, this list covers the most frequently encountered vocabulary in pool ownership, maintenance, and care.

A

Acid Demand

• The amount of acid required to lower the pH of pool water to the proper level, determined by testing with an acid demand reagent.

Acid Wash

• A process of cleaning pool surfaces (especially plaster or pebble finishes) with a diluted acid solution to remove stains and mineral deposits.

Algae

• Microscopic plant-like organisms that can grow in pool water if not properly sanitized. Common types include green, mustard (yellow), and black algae.

Algaecide

• Algaecide is a chemical used to kill or prevent algae growth in pool water. Different formulations target different algae types.

Alkalinity (Total Alkalinity)

• Total alkalinity is measure of the water’s ability to neutralize acids, helping buffer pH fluctuations. Typically measured in parts per million (ppm), ideal range is usually 80–120 ppm.

Automatic Pool Cleaner

• A device (suction, pressure, or robotic) that automatically removes debris from the pool floor, walls, and sometimes waterline.

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B

Backwash

• Backwash is the process of reversing water flow through a pool filter (usually sand or DE filter) to remove trapped debris and clean the filter media.

Baking Soda (Sodium Bicarbonate)

• Baking Soda is common chemical used to raise total alkalinity (and sometimes to fine-tune pH) in pool water.

Balanced Water

• When pH, total alkalinity, calcium hardness, and sanitizer levels are all within recommended ranges, minimizing scaling, corrosion, and cloudy water.

Bather Load

• The number of swimmers using the pool at a given time, which affects chemical consumption and filtration needs.

Bromine

• Bromine is a halogen sanitizer alternative to chlorine, often used in spas or indoor pools because it remains stable at higher temperatures.

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C

Calcium Hardness

• The amount of dissolved calcium in the water. Low calcium can cause corrosion, while high calcium can lead to scale formation. Typically measured in ppm, an ideal range is about 200–400 ppm.

Cartridge Filter

• A type of pool filter that uses replaceable or cleanable cartridges of polyester or paper-like material to capture debris.

Chloramine (Combined Chlorine)

• Compounds formed when free chlorine combines with ammonia or organic contaminants. Causes strong “chlorine” odor and eye irritation; removed by breakpoint chlorination (shock).

Chlorine

• The most commonly used sanitizer for swimming pools. Can come in liquid, granular, or tablet form.

Chlorine Demand

• The amount of chlorine required to oxidize all contaminants in the water, including bacteria, algae, and organic debris, to reach a safe free chlorine level.

Circulation

• The process of moving pool water through the pump, filter, and back into the pool to maintain cleanliness and chemical distribution.

Clarifier

• A chemical that coagulates or clumps small particles so they can be more easily filtered out, resulting in clearer water.

Coping

• The cap or edging at the top of a pool wall or deck area, often made of stone, concrete, or special pool edging materials.

Cyanuric Acid (Stabilizer or Conditioner)

• Cyanuric acid (CYA) is a chemical added to outdoor pools to protect chlorine from degradation by UV rays. Ideal range is typically 30–50 ppm.

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D

Diatomaceous Earth (DE)

• A finely ground fossilized material used as a filter media in DE filters to trap very small particles, producing highly clear water.

DPD Test

• A method of testing chlorine or bromine levels in pool water, producing a pink color; measured by color matching or via titration (FAS-DPD).

Drain

• The main outlet at the bottom of the pool to remove water from the deepest part. Also refers to the act of lowering or emptying water from the pool.

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E

Electrolytic Chlorine Generator (Saltwater Chlorinator)

• A system that uses salt dissolved in pool water and an electrical cell to generate chlorine, providing continuous sanitation.

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F

Filtration

• The process of circulating pool water through a filter (sand, cartridge, or DE) to remove debris and particles.

Flocculant (Floc)

• Flocculant is a chemical that binds small suspended particles into larger clumps that sink to the bottom, allowing them to be vacuumed out.

Flow Rate

• The amount of water passing through the pool filtration system in a given time, typically measured in gallons per minute (GPM).

Foam

• Foam is the bubbles or froth on the pool surface, often caused by soaps, lotions, or imbalanced chemicals.

Free Chlorine

• The active form of chlorine available in the water to sanitize and oxidize contaminants, not yet bound to other molecules.

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G

Gunite

• A mixture of cement, sand, and water sprayed over rebar to create a concrete pool shell (often interchangeably called “shotcrete,” though they have technical differences).

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H

Hardness

• See “Calcium Hardness.”

Heater

• A gas, electric, or heat pump system used to heat pool water, extending the swimming season or providing comfort in cooler climates.

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I

Ionizer

• A device that releases copper and/or silver ions into the pool water to help control algae and bacteria, usually used in conjunction with low-level chlorine or oxidizer.

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L

Langelier Saturation Index (LSI)

• A calculated number that helps predict whether water will deposit calcium carbonate (scale) or dissolve it (corrosive). Uses pH, total alkalinity, calcium hardness, temperature, and TDS to evaluate water balance.

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M

Main Drain

• The drain at the deepest area of the pool, responsible for pulling water into the filter system from the bottom. Modern systems often feature dual main drains for safety.

Muriatic Acid (Hydrochloric Acid)

• Muriatic acid is a strong acid used to lower pH and total alkalinity, and for acid washing pool surfaces.

Multiport Valve

• A multiport valve on sand or DE filters directs water flow for various operations, including filter, backwash, rinse, waste, recirculate, and closed positions.

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O

ORP (Oxidation-Reduction Potential)

• A measure of the water’s ability to oxidize contaminants. Often used with automated chemical feeders to maintain consistent sanitizer levels.

O-Ring

• A circular rubber gasket used to create a watertight seal in pumps, filters, and other pool equipment.

Oxidation

• The chemical process in which contaminants such as oils, lotions, and organic debris are destroyed by sanitizer (chlorine or other oxidizers).

Ozone

• A strong oxidizer created by an ozone generator. Used as a supplement to chlorine or bromine to reduce overall chemical usage and improve water clarity.

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P

pH

• A measure of the acidity or alkalinity of the pool water. Ranges from 0–14, with 7.4–7.6 considered ideal for comfort and sanitizer efficiency.

Plaster

• A common interior finish for concrete and gunite pools. Sometimes mixed with aggregates (pebble, quartz) for enhanced appearance and durability.

Phosphate

• A nutrient that can feed algae growth, often introduced by debris or fertilizers; removable with a phosphate remover.

Pool Brush

• A pool brush is a tool with stiff bristles used to scrub pool walls, steps, and floors to remove algae and stains.

Pool Cover

• A cover placed over the pool to reduce evaporation, maintain heat, prevent debris, or provide safety. Types include solar covers, safety covers, and winter covers.

Pool Net

• A pool net is used to remove leaves from the surface of the water. Many have a scoop which allows leaves to be removed from the bottom of the pool.

Pool Shock

• The process of adding a large dose of chlorine (shock) or other oxidizer to eliminate chloramines, kill bacteria and algae, and clear cloudy water.

PPM (Parts Per Million)

• The standard unit of measurement for chemical concentration in pool water, e.g., chlorine at 2–4 ppm.

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R

Return Inlets (Return Lines)

• Fittings on pool walls or floors where filtered water re-enters the pool after passing through the pump and filter.

Robotic Pool Cleaner

• A robotic pool cleaner is a self-contained, electric-powered cleaner with an internal filter, capable of scrubbing pool floors, walls, and sometimes tile lines.

Run Time

• The duration a pool pump operates daily to maintain circulation and filtration (typically 8-12 hours).

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S

Safety Cover

• A strong mesh or solid cover anchored around the pool, capable of supporting weight to prevent accidental entry when the pool is not in use.

Salt Chlorinator (Saltwater System)

• See “Electrolytic Chlorine Generator.”

Sand Filter

• A filter that uses specifically graded sand as the filtration medium. Water passes through the sand, trapping debris before returning to the pool.

Scale

• The buildup of calcium or other minerals on pool surfaces, plumbing, and equipment, often resulting from high pH or high calcium hardness.

Shock Treatment

• An alternative term for pool shock; dosing the pool with a large amount of sanitizer to quickly oxidize contaminants.

Skimmer

• A device built into the side of a pool that draws in water from the surface to trap floating debris in a skimmer basket or sock. Normally one skimmer has two holes open at the bottom and the others only one.

Soda Ash (Sodium Carbonate)

• Soda ash is a chemical used to raise pH in pool water (also raises total alkalinity to some degree).

Solar Cover

• A pool solar cover floats on top of the pool to retain heat and reduce water evapouration.

Stabilizer

• Another term for cyanuric acid, which protects chlorine from UV breakdown in outdoor pools.

Strainer Basket

• A basket in the pump or skimmer that catches larger debris like leaves, preventing them from entering and clogging the pump or filter.

Suction Line

• The plumbing that draws water from the pool into the pump and filter system.

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T

TDS (Total Dissolved Solids)

• The total concentration of dissolved substances in the water. Excessively high TDS can interfere with sanitizer effectiveness and cause cloudy water.

Test Kit/Strip

• Tools used to measure chemical levels (pH, chlorine/bromine, alkalinity, hardness, and more) in pool water.

Tile Line

• The band of tile at the waterline in a gunite or concrete pool, which helps prevent staining and simplifies cleaning at the water’s edge.

Total Alkalinity (TA)

• The measure of alkaline substances in water that buffer pH changes (ideal range: 80-120 ppm).

Turbidity

• Cloudiness in pool water caused by suspended particles or poor filtration.

Turnover Rate

• The time it takes for the pool’s volume of water to circulate once through the filtration system (commonly targeted at 6–8 hours for residential pools).

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U

UV Sanitizer

• A system that passes circulating water by a UV lamp, where ultraviolet light kills or inactivates microorganisms, reducing chemical needs.

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V

Vacuum

• A manual or automatic method of removing debris from the pool floor. Manual vacuums attach to a telescopic pole and use the pool’s pump or a separate vacuum pump.

Variable Speed Pump

• A variable speed pump is an energy-efficient pump that adjusts its speed to optimize circulation and reduce electricity costs.

Vinyl Liner

• A soft, flexible plastic liner that forms the interior surface of many above-ground and some in-ground pools.

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W

Water Balance

• The overall state of the pool water when key factors (pH, alkalinity, calcium hardness, sanitizer levels, and temperature) are within recommended parameters.

Weir

• A floating or pivoting door in the skimmer that controls water flow into the skimmer and prevents debris from floating back into the pool.

Winterizing

• Winterizing is the process of preparing a pool for cold weather, including lowering the water level, adding winter chemicals, and covering the pool to prevent damage.

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Z

Zinc Anode

• A sacrificial metal piece often placed in saltwater systems or attached to pool hardware to combat corrosion by electrolysis.