Pool glossary

196 pool and spa terms in plain English, from free chlorine to freeze guard. Chemistry numbers link to their sources.

A

Acid wash: An acid wash cleans a plaster pool by removing a thin layer of surface with a diluted acid solution.
Air leak: An air leak is a spot where air is sucked into the system, causing bubbles and weak flow.
Air relief valve: The air relief valve is a small valve on top of the filter that releases trapped air.
Algaecide: Algaecide is a chemical that kills or prevents algae, but it does not replace chlorine.
Automatic pool cleaner: An automatic pool cleaner is a machine that cleans the floor and walls on its own.
Automatic water leveler: An automatic water leveler is a device that adds fresh water to the pool when the level drops too low.

B

Backflow: Backflow is water flowing the wrong way into a clean water supply.
Backwash: Backwash means reversing flow through a sand or DE filter to flush out dirt.
Black algae: Black algae shows up as dark spots with deep roots, often in plaster, and needs hard brushing and treatment.
Bonding: Bonding is wiring that ties the metal parts around a pool together so they stay at the same electrical potential.
Booster pump: A booster pump is a small extra pump that powers a pressure-side cleaner.
Borates: Borates are a water additive some owners use to buffer pH and help prevent algae.
Breakpoint chlorination: Breakpoint chlorination means adding enough chlorine to destroy chloramines and reset the water.
Bromine: Bromine is a sanitizer often used in hot tubs because it holds up well in heat.
Bucket test: A bucket test compares water loss in a bucket on the pool step with water loss in the pool to spot leaks.

C

Calcium hardness: Calcium hardness is the amount of dissolved calcium in pool water, and it affects scale and surface wear.
Calcium hypochlorite: Calcium hypochlorite, or cal-hypo, is a granular chlorine that adds calcium to the water.
Capacitor: A capacitor is a part that helps a pump motor start, and a weak one causes humming and no start.
Cartridge filter: A cartridge filter uses pleated fabric cartridges that you rinse with a hose or replace when worn.
Cavitation: Cavitation is noise and damage caused when a pump starves for water.
Check valve: A check valve is a one-way valve that stops water flowing backward.
Chemical surcharge: A chemical surcharge is an extra fee some pool companies add for chemicals. Ask if one applies.
Chemical-only service: Chemical-only service is a plan that tests and adds chemicals but does not clean the pool.
Chloramine: Chloramines are compounds formed when chlorine bonds with nitrogen from sweat and urine, causing the strong pool smell and eye irritation.
Chlorine demand: Chlorine demand is the amount of chlorine the water uses up before any is left to sanitize.
Chlorine floater: A chlorine floater is a floating plastic dispenser that holds chlorine tablets and releases them slowly into the pool.
Chlorine lock: Chlorine lock is a state where very high cyanuric acid makes chlorine work poorly.
Chlorine odor: Chlorine odor is a strong smell that usually signals chloramines, not too much chlorine.
Clarifier: A clarifier is a product that clumps tiny particles so the filter can catch them.
Cloudy water: Cloudy water is hazy water caused by tiny particles, poor filtration, or unbalanced chemistry.
Combined chlorine: Combined chlorine is chlorine that has already bonded with sweat, oils, and other waste, so it no longer sanitizes well.
Control panel: The control panel is the box or screen where pool equipment is switched and scheduled.
Coping: Coping is the cap along the pool edge where the pool wall meets the deck.
Copper ionizer: A copper ionizer is a device that adds copper to the water to slow algae, and chlorine is still needed.
CPO certification: CPO certification is the Certified Pool Operator credential from the Pool and Hot Tub Alliance.
Cryptosporidium: Cryptosporidium is a chlorine-tolerant germ that can cause illness in pools. CDC has guidance on it.
Cyanuric acid: Cyanuric acid, also called CYA, stabilizer, or conditioner, shields chlorine from sunlight.

D

DE filter: A DE filter uses diatomaceous earth powder to catch very fine particles.
Deck-O-Seal: Deck-O-Seal is a brand of flexible joint sealant used between pool coping and the surrounding deck.
Delamination: Delamination is when a pool finish lifts, peels, or sounds hollow as it separates from the shell.
Diagnostic fee: A diagnostic fee is a charge to find a problem. It may or may not be credited to the repair.
Dichlor: Dichlor is a fast-dissolving granular chlorine that also adds cyanuric acid to the water with each dose.
Drain cover: A drain cover is the grate over a pool drain. Approved designs help prevent suction entrapment.
Drop test kit: A drop test kit uses liquid reagents, such as FAS-DPD, to give more exact water readings than strips.
Drought: A drought is a long dry spell that raises evaporation and water supply concerns.

E

Efflorescence: Efflorescence is a white, powdery mineral deposit that seeps out of concrete, stone, or grout.
Enzyme treatment: An enzyme treatment is a product that breaks down oils and organic waste in the water.
Equalizer line: An equalizer line is a pipe that links the skimmer to the pool so the pump cannot run dry if the water drops.
Equipment inspection: An equipment inspection is a check that the pump, filter, heater, and controls work as they should.
Equipment upgrade: An equipment upgrade is replacing old equipment with a newer, more efficient model.
Equipment warranty: An equipment warranty is the maker's promise to cover defects for a set time.
Etching: Etching is loss of surface material from plaster or tile when the water is acidic or aggressive.
Evaporation loss: Evaporation loss is the normal water loss from heat, wind, and sun that is not a leak.
Expansion joint: An expansion joint is a gap between the pool and the deck that lets each material move without cracking.

F

Fiberglass pool: A fiberglass pool is a pool made from a one-piece molded fiberglass shell set into the ground.
Fill water: Fill water is the tap or well water used to top off the pool, and its chemistry affects the pool.
Filter cleaning: Filter cleaning is a deep clean or replacement of filter media so the filter can trap dirt again.
Filter grids: Filter grids are the fabric panels inside a DE filter that hold the powder.
Filter sand: Filter sand is the special-grade sand inside a sand filter, and it wears out over years.
Flocculant: A flocculant is a product that drops fine particles to the pool floor to be vacuumed out.
Flow switch: A flow switch is a sensor that confirms water is moving through a salt cell or heater.
Free chlorine: Free chlorine is the chlorine in pool water that is still active and ready to kill germs and algae right now.
Free estimate: A free estimate is a price quote with no charge for the visit.
Freeze: A freeze is air temperature at or below 32 degrees Fahrenheit, the point where water turns to ice.
Freeze guard: Freeze guard is a control that starts the pump when the air gets cold to keep water moving.
Freeze protection: Freeze protection is a set of steps that keep water moving or drained so equipment does not freeze.
Freeze sensor: A freeze sensor is a sensor that reads air temperature for freeze protection.
Full-service plan: A full-service plan is a pool care plan where the company handles both cleaning and chemicals.

G

Gas heater: A gas heater burns natural gas or propane to heat pool water quickly.
GFCI: A GFCI is a ground fault circuit interrupter, an outlet or breaker that cuts power fast when it detects a shock hazard.
Green algae: Green algae is the most common pool algae, and it turns water green and can bloom within days.
Green pool cleanup: A green pool cleanup is a one-time deep clean that turns algae-filled water back to clear.
Gunite: Gunite is concrete sprayed dry through a hose with water added at the nozzle, used to build many pool shells.

H

Hail: Hail is falling ice stones that can damage pool covers, lights, and equipment housings.
Hairline crack: A hairline crack is a very thin crack in the surface finish that is often cosmetic.
Hard freeze: A hard freeze is a longer, colder freeze that can crack pipes, pumps, filters, and heaters.
Hard water: Hard water is water with high calcium and minerals that can leave scale.
Heat exchanger: The heat exchanger is the part of a heater that passes heat into the pool water.
Heat pump: A heat pump is an electric heater that moves heat from the air into the water.
Heat wave: A heat wave is several days of very high heat that raise chlorine use and water temperature.
Hot tub: A hot tub is a self-contained heated tub with its own heater, pump, and filter, built for soaking.

I

Igniter: The igniter is the part that lights the gas burner in a heater.
Impeller: The impeller is the spinning part inside the pump that moves water.
Inline chlorinator: An inline chlorinator is a feeder in the plumbing that dissolves chlorine tablets.
IPSSA: IPSSA is the Independent Pool and Spa Service Association, a trade group for pool service pros.

L

Lab water test: A lab water test is a full water analysis from a pool store or a service company.
Langelier Saturation Index: The Langelier Saturation Index is a number that predicts whether pool water will scale or etch surfaces.
Leak detection: Leak detection is the work of finding where a pool or its plumbing loses water.
LED pool light: An LED pool light is a low-energy underwater light that lasts a long time and can show many colors.
Liability insurance: Liability insurance is coverage that pays for damage a contractor causes on a job.
Lid O-ring: The lid O-ring is the rubber ring that seals the pump lid and keeps air out.
Light niche: A light niche is the housing set in the pool wall that holds the pool light and its cord.
Liquid chlorine: Liquid chlorine is sodium hypochlorite in liquid form, and it adds chlorine without adding cyanuric acid.
Live oak debris: Live oak debris is the leaves and catkins that live oak trees drop and that load skimmers and filters.

M

Main drain: The main drain is the drain at the deepest point of the pool that pulls water down to the pump.
Metal stain: Metal stains are brown, green, or purple marks caused by iron, copper, or other metals in the water.
Mosquito breeding: Mosquito breeding happens in standing water, including neglected pools, where mosquitoes lay eggs.
Motor bearings: Motor bearings are parts that let the motor shaft spin, and worn ones make a screaming sound.
Multiport valve: A multiport valve is a valve on a sand or DE filter that sets filter, backwash, rinse, and other modes.
Muriatic acid: Muriatic acid is a strong acid used to lower pH and total alkalinity.
Mustard algae: Mustard algae is a yellow-brown algae that clings to shady walls and resists normal chlorine.

O

One-time cleaning: A one-time cleaning is a single pool clean with no weekly contract.
Oxidizer: An oxidizer is a chemical that breaks down organic waste in the water, and chlorine is one.

P

Partial drain and refill: A partial drain and refill replaces some of the pool water to lower cyanuric acid, calcium, or salt.
Parts and labor: Parts and labor are the two main charges on a repair bill: the items replaced and the time to do the work.
Pebble finish: A pebble finish is a pool surface made of small natural stones mixed into cement.
pH: pH is a scale that shows how acidic or basic water is, and it affects chlorine strength and swimmer comfort.
Phosphates: Phosphates are a nutrient that can feed algae growth in pool water.
PHTA: PHTA is the Pool and Hot Tub Alliance, a US trade group that sets industry standards.
Pink slime: Pink slime is a pink bacteria film often found in shaded spots, fittings, and low-flow areas.
Plaster: Plaster is a mix of white cement and marble dust used as the smooth interior finish of many concrete pools.
Pollen season: Pollen season is the spring and fall time when tree pollen coats pool water and clogs filters.
Pool alarm: A pool alarm is a device that sounds when someone enters the water or a door to the pool opens.
Pool automation: Pool automation is a control system that runs the pump, lights, heater, and more from a panel or app.
Pool barrier: A pool barrier is a fence or wall meant to keep children away from the water.
Pool closing: Pool closing is shutting a pool down for a season. Many North Texas owners keep their pools running instead.
Pool deck: The pool deck is the surface around the pool, often concrete, travertine, or pavers.
Pool filter: The pool filter is the equipment that traps dirt and fine particles from the water.
Pool heater: A pool heater is equipment that warms pool water, usually gas or a heat pump.
Pool inspection: A pool inspection is a check of the equipment, surfaces, and safety features, often before a sale or repair.
Pool light: A pool light is a waterproof fixture mounted in the pool wall that lights the water for night swimming and safety.
Pool mastic: Pool mastic is the common name for the flexible sealant that fills the joint between pool coping and the deck.
Pool opening: Pool opening is restarting a pool after it was closed or sat idle for a season.
Pool plumbing: Pool plumbing is the network of pipes and fittings that carry water between the pool and the equipment.
Pool pump: The pool pump moves water through the filter, heater, and chlorine system, and back to the pool.
Pool technician: A pool technician is a trained person who services pools, tests the water, and repairs equipment.
Pool timer: A pool timer is a clock that turns the pump or other equipment on and off at set times.
Post-storm algae: Post-storm algae is an algae bloom that follows rain, when chlorine is diluted and nutrients are added.
Power center: The power center is the electrical box that powers and controls pool equipment.
Pressure gauge: The pressure gauge is a gauge on the filter that shows system pressure and signals when to clean.
Pressure switch: A pressure switch is a safety part that tells the heater water is flowing.
Pressure test: A pressure test checks pool plumbing lines for leaks by filling them with pressure and watching for a drop.
Pressure-side cleaner: A pressure-side cleaner is driven by a return line or a booster pump.
Priming: Priming is filling the pump with water so it can start pulling.
Pump basket: The pump basket is a basket inside the pump that catches debris before it reaches the impeller.
Pump motor: The pump motor is the sealed electric motor that turns the impeller and drives water through the system.

Q

Quartz finish: A quartz finish is a pool surface of crushed quartz mixed into cement.

R

RAIL license: A RAIL license is the Texas Residential Appliance Installer License, which allows limited electrical work on residential appliances, including pool equipment.
Recreational water illness: Recreational water illness is sickness caused by germs in pools, spas, and splash areas.
Resurfacing: Resurfacing is replacing the interior finish of a pool, such as plaster, pebble, or quartz.
Return jet: A return jet is the fitting in the pool wall where filtered, treated water flows back into the pool.
Robotic cleaner: A robotic cleaner is a self-contained cleaner with its own motor and filter bag.

S

Safety cover: A safety cover is a strong, tight cover that blocks access to the pool when no one is swimming.
Salt cell: The salt cell holds the plates inside a salt chlorine generator that make chlorine, and it wears out over time.
Salt chlorine generator: A salt chlorine generator turns dissolved salt into chlorine inside the pool plumbing.
Salt level: Salt level is the parts per million of salt in a saltwater pool, and the cell maker sets the target.
Salt system conversion: A salt system conversion changes a chlorine pool to run on a salt chlorine generator.
Sand filter: A sand filter uses sand as the filter media, and you clean it by backwashing.
Sanitizer: A sanitizer is a chemical that kills germs in pool water, and in most pools it is chlorine.
Scale: Scale is hard white or gray calcium buildup on tile, surfaces, and equipment.
Service call: A service call is a visit to diagnose or fix a problem.
Service log: A service log is a record of tests, doses, and work done at each pool visit.
Service route: A service route is the set of pools a technician visits on a given day.
Shaft seal: The shaft seal is a small seal that stops water from leaking along the motor shaft.
Shock: Shock is a large one-time dose of chlorine or another oxidizer used to clear chloramines, bacteria, or algae.
Shotcrete: Shotcrete is concrete mixed wet with water first and then sprayed to build pool shells.
Single-speed pump: A single-speed pump runs at one fixed speed, and newer federal rules limit new sales.
Skimmer: The skimmer is the opening in the pool wall that pulls surface water and debris into the system.
Skimmer basket: The skimmer basket is a basket in the skimmer that catches leaves and debris from the surface.
Soda ash: Soda ash is sodium carbonate, a pool product used to raise a low pH back into range.
Sodium bicarbonate: Sodium bicarbonate is plain baking soda, and pool owners use it to raise low total alkalinity.
Sodium bisulfate: Sodium bisulfate is a dry acid used to lower pH and total alkalinity.
Spa: A spa is a small heated pool for soaking, often joined to a larger pool.
Spa blower: A spa blower is a device that pushes air into spa jets to make bubbles.
Spa jets: Spa jets are nozzles that push water or air into a spa for massage.
Spillway: A spillway is a spot where water flows over an edge, such as from a spa into a pool.
Stabilizer: Stabilizer is another name for cyanuric acid, and it slows chlorine loss in sunlight.
Startup service: A startup service is a visit to restart a pool and its equipment after a long idle period.
Storm runoff: Storm runoff is rain that carries dirt, pollen, and nutrients into the pool.
Structural crack: A structural crack is a wider crack that may mean the shell is moving or leaking.
Suction entrapment: Suction entrapment is a hazard where strong suction at a drain traps a swimmer under water.
Suction-side cleaner: A suction-side cleaner is an automatic pool cleaner that runs off the pump's suction line through the skimmer.
Swim season: Swim season is the months a pool gets used. In North Texas this often runs from spring to fall.

T

Tanning ledge: A tanning ledge is a shallow shelf in the pool, often for lounging chairs or kids.
TDLR: TDLR is the Texas Department of Licensing and Regulation, which licenses some pool-related electrical work.
Test strips: Test strips are paper strips that change color to give a quick estimate of water chemistry.
Thermostat: A thermostat is the control that sets and reads pool water temperature.
Total alkalinity: Total alkalinity is the water's ability to resist pH changes, and it works as a pH buffer.
Total chlorine: Total chlorine is the sum of free chlorine and combined chlorine, as shown on a standard chlorine test.
Total dissolved solids: Total dissolved solids, or TDS, is the total of everything dissolved in the water.
Transformer: A pool light transformer is a device that lowers household voltage to a safer, lower voltage for some pool lights.
Trichlor: Trichlor is a slow-dissolving chlorine tablet that also adds cyanuric acid and lowers pH.
Two-speed pump: A two-speed pump has a high speed and a low speed setting.

U

Union fitting: A union fitting is a threaded joint in pool plumbing that you can unscrew so equipment can be removed for service.
UV exposure: UV exposure is strong sunlight that breaks down chlorine quickly when the water has no stabilizer.

V

Vacation service: Vacation service is routine pool care that keeps the water safe and clear while the owner is away.
Valve actuator: A valve actuator is a small motor on a pool valve that lets an automation system turn the valve for you.
Variable-speed pump: A variable-speed pump runs at adjustable speeds and uses much less power at low speeds.
Vinyl liner pool: A vinyl liner pool is a pool with a sheet of vinyl stretched over a wall frame and a sand or concrete floor.

W

Water balance: Water balance is the right mix of pH, alkalinity, hardness, and stabilizer for safe, clear water.
Water feature: A water feature is a waterfall, fountain, or scupper that moves water for looks and sound.
Water restrictions: Water restrictions are city limits on outdoor water use that can affect filling and draining a pool.
Waterline tile: Waterline tile is the band of tile at the water's edge that resists stains, oils, and scale.
Weekly pool service: Weekly pool service is a routine visit that tests the water, balances chemicals, and cleans the pool.
Wind debris: Wind debris is the leaves, dust, and trash that strong winds blow into the pool.
Winterization: Winterization is the work of preparing a pool and its equipment so they survive freezing weather.

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