Swimming Pool Terms Glossary



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Salt Generator An electrical device that generates chlorine from a salt (sodium chloride, NaCl) solution in a tank or from salt added to the pool water. Sometimes called a chlorine generator or electrolytic cell.

Salt Water Water containing relatively high concentration of salt, usually over 1,000 ppm or mg/L but less than the sea. The ocean has about 35,000 ppm of TDS.

Sand Usually refers to the filter medium used by a sand filter. The grade most often specified by filter manufacturers is grade #20 with a particle size of 45 to 55 mm (millimeters).

Sand Filter A filter using sand or sand and gravel as the filter medium. The oldest (patented in 1790) method of improving water quality, generally using two layers of sand supported by an underbed layer of gravel.

Sanitize To render sanitary; to kill all living things including bacteria and algae. Similar to sterilize.

Saturation – also called the saturation point – The condition of the water when it has taken into solution the maximum possible quantity of a given substance at a given temperature, alkalinity and pH. Water hardness is calcium and magnesium dissolved in the water. When the water can hold no more of these elements, they deposit or precipitate out of the water causing scale. Other elements that can be saturated in pool and spa water are copper and iron. Usually, as the pH and alkalinity rise, the elements become less soluble causing them to come out of solution.

Saturation Index (SI) The relation of calcium carbonate to the pH, alkalinity and hardness of a given water to determine its scale forming tendency. Employs the use of factors and values for five constituents of the water (pH, alkalinity, hardness, TDS and temperature) substituted into a mathematical equation.

Scale The precipitate that forms on surfaces in contact with water when the calcium hardness, pH or total alkalinity levels are too high. Results from chemically unbalanced pool and spa water. Scale may appear as grey, white, or dark streaks on the plaster, fiberglass or vinyl. It may also appear as a hard crust around the tile.

Scale Inhibitor A chemical added to the water that prevents scale from forming.

Seal Packing gland material or a mechanical device that fits around a pump shaft and prevents either air intake to the pump or water leakage.

Scum The extraneous or foreign matter which rises to the surface of the water and forms a layer or film there. It can also be a residue deposited on the tile or walls of the pool or spa. Sources of scum are soap, oil, deodorant, hair spray, sun tan lotion and various others.

Sediment Solid material settled out from the water.

Sediment Trap A device for trapping sediment that is required on all gas heaters.

Self-Priming A classification given to centrifugal pumps that indicates the pump is capable of operating above the pool water level after initially filling with water. Most self-priming pumps have a hair and lint strainer basket attached to the front of the pump.

Sensor An electrical or electronic device that measures water quality. Examples are pH electrodes, pH meters, ORP (Oxidation Reduction Potential) probes and meters, TDS meters and probes.

Separation Tank A container used in conjunction with a DE filter to trap DE and dirt when backwashing.

Sequestering Agent / stain inhibitor – A chemical that will combine with dissolved metals in the water to prevent the metals from coming out of solution (precipitating or causing stains). May also be a chemical that removes dissolved metals from water. Leslie’s Stain & Scale

Shock Treat The practice of adding significant amounts of an oxidizing chemical (usually non-chlorine oxidizers such as sodium persulfate or potassium peroxymonosulfate) to the water to destroy ammonia and nitrogen compounds or swimmer waste. Shock treat used to mean superchlorinating to 10-20 ppm of free chlorine.

Silver Algaecide Algaecides that have colloidal silver or silver ions as their active ingredient.

Skimmer A device installed through the wall of a pool or spa that is connected to the suction line of the pump that draws water and floating debris in from the surface of the water. The skimmer basket catches large debris while the filter traps smaller particles.

Skimmer Basket A removable, slotted basket or strainer placed in the skimmer on the suction side of the pump, which is designed to trap floating debris in the water flow from the surface without causing much flow restriction.

Skimmer Weir Part of a skimmer that adjusts automatically to small changes in water level to assure a continuous flow of water to the skimmer. The small floating "door" on the side of the skimmer that faces the water over which water flows on its way to the skimmer.

Slime Any of numerous substances of viscous organic nature that are usually formed from microbial growth and that attach themselves to other objects, forming a coating.

Soda Ash See sodium carbonate.

Sodium Bicarbonate (baking soda or bicarb] Used to raise total alkalinity in pool and spa water with only a slight affect on the pH.

Sodium Bisulfate (dry acid] A chemical used to lower the pH and total alkalinity. 2 1/2 pounds of dry acid are equal to 1 quart of muriatic acid.

Sodium Bromide A salt of bromine, chemical formula NaBr. It is used to establish a bromide "bank" in pool and spa water prior to beginning the use of bromine tablets.

Sodium Carbonate (common name, soda ash) A chemical used to raise the pH and total alkalinity in pool and spa water.

Sodium Dichlor Common name for sodium dichloro-s-triazinetrione. A fast-dissolving, granular, stabilized organic chlorine compound providing either 56% or 63% available chlorine. Used for regular as well as superchlorination. Contains an ingredient (cyanuric acid or stabilizer) that prevents the chlorine from being destroyed by the ultraviolet (UV) rays of the sun.

Sodium Hypochlorite Liquid chlorine, hypochlorite solution, chemical formula NaOCl; usually provides 10-12% available chlorine (or about 1 lb. of pure chlorine per gallon); has a pH of 13 and requires that small amounts of acid be added to the pool to neutralize the high pH. Good for regular chlorination and superchlorination. Not recommended for spas. Does not contain conditioner or stabilizer to protect it from sunlight but it is protected if stabilizer or conditioner is already in the water.

Soft Water Water that has a very low calcium and magnesium content (water hardness) – usually means less than 100 ppm or 6 grains. Also, water that has gone through a water softener. Pools and spa should never be filled with soft water from a softener. Water with less than 100 ppm of hardness should be increased to a minimum of 150 to 200 ppm using calcium chloride.

Solar Cover A cover that when placed on the water's surface of a pool, spa or hot tub, increases the water temperature by absorption and transmission of solar radiation, reduces evaporation and prevents wind-borne debris from entering the water.

Solar Heating System Usually panels or coils of plastic or metal through which water passes to increase the temperature from the sun's radiant heat.

Solenoid Valve An electrical device operated by a magnetic coil to make the valve either open for flow or closed to shut off water flow.

Source Water – also called "tap" water – It is the water used to fill or refill the pool or spa.

Spring Board – also called a "diving board" – A recreational mechanism for entering a swimming pool consisting of a semirigid board that derives its spring from a fulcrum mounted below the board and attached to the deck.

Stabilized Chlorine A family of chlorine pool sanitizers that contain conditioner (cyanuric acid or isocyanuric acid) to protect the chlorine from the degrading UV rays in sunlight. Most common types are sodium dichlor and trichlor ("dichlor" and "trichlor"). Granular form is dichlor which is fast dissolving and can be used for regular chlorination or superchlorination by broadcasting into the pool or spa. Tablet or stick form is trichlor which is usually used in a chlorine feeder either the floating type or the in-line erosion type used for regular chlorination only.

Stabilizer – also known as conditioner – See cyanuric acid.

Stain A discoloration or a colored deposit on the walls or bottom of a swimming pool or spa. Most often stains are metallic oxides, hydroxides, carbonates, sulfates, silicates and phosphates of such metals as iron, copper and manganese. They may appear as green, gray, brown or black. They may even discolor the water. Sometimes a sequestering agent or chelating agent will remove them. If not, usually an acid wash is necessary to remove them from the walls and bottom. The metals get in the water because the pH was too low or someone has added a low-pH chemical directly into the circulation system. The low-pH chemical then dissolves a small amount of metal from the equipment. Then, under certain conditions, the metals begin to come out of solution and deposit or stain the walls and bottom. Stains are sometimes confused with scale which is a deposit of calcium or magnesium on the walls, bottom or in the equipment.

Sterilize To destroy or kill by any of several means all living microorganisms in water.

Strainer Basket An easily removable perforated or otherwise porous container used to catch coarse material such as leaves, twigs, insects and other debris before it gets into the pump.

Sump A tank or pit that receives drainage and stores it temporarily and from which the discharge is pumped or ejected.

Superchlorination The practice of adding an extra large dose (5-10 ppm) of chlorine to the water to destroy ammonia, nitrogen and swimmer waste which can build up in the water. This level of chlorine is required to destroy all of the combined chlorine in the water, which is called break-point chlorination. Technically it requires 7.6 moles of chlorine for each mole of ammonia to reach breakpoint chlorination. If the ratio of 7.6:1 is not reached, ammonia destruction does not happen. Common practice in the pool and spa industry is to multiply the amount of combined chlorine times 10 and add that amount of chlorine to the water. This way you are sure the ratio has been met and there is some chlorine left over to provide a residual.

Surface Area The two-dimensional area of an object. The surface area of a pool is just the length times the width – no depth. The surface of the water. Also refers to the filter surface area.

Surge Tank A tank that accumulates water in response to a pressure surge and supplies water in instances of moderate negative gauge pressure, thereby preventing damage to pumping and piping equipment.

Swimout A recessed area outside the general perimeter of a pool. Swimouts are designed to allow entry and exit from the pool.



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