Quick Answer
Pool ownership comes with its own vocabulary. This page defines every term you’ll encounter — from alkalinity to weir — so you never have to wonder what the pool store guy is talking about. Bookmark this one.
What You Need To Know
The 10 Terms Every Pool Owner Must Know
These are the ones that come up every single week:
- Free Chlorine (FC) — The active chlorine in your water that’s available to kill bacteria and algae. This is the number you’re testing for. Target: 1–3 ppm for traditional chlorine pools, 1–5 ppm acceptable for salt water. See our Chlorine Guide.
- pH — How acidic or basic your water is, on a 0–14 scale. Pool target: 7.4–7.6. Low pH (acidic) corrodes equipment and irritates skin. High pH reduces chlorine effectiveness and causes cloudy water. Full detail in pH, Alkalinity, and Calcium.
- Total Alkalinity (TA) — Acts as a buffer for pH, preventing it from swinging wildly. Target: 80–120 ppm. Adjust this before adjusting pH.
- Cyanuric Acid (CYA) / Stabilizer — Protects chlorine from being destroyed by UV sunlight. Target: 30–50 ppm. Without it, you’ll burn through chlorine in hours on a sunny day. See our CYA Guide.
- Shock / Shocking — Adding a large dose of chlorine (or non-chlorine oxidizer) to destroy chloramines, kill algae, and reset your water. Done weekly or after heavy pool use.
- ppm (parts per million) — The unit of measurement for pool chemicals. 1 ppm = 1 milligram per liter. All your test results are in ppm.
- Turnover — The time it takes for your pump to circulate the entire pool volume through the filter. You want at least 1 full turnover per day (8-12 hours of pump run time for most residential pools).
- Skimmer — The rectangular opening at the waterline of your pool that pulls in floating debris (leaves, bugs, pollen). Contains a basket you empty regularly.
- Return Jets / Returns — The round fittings in the pool walls where clean, filtered water flows back into the pool. Angle them to create circulation patterns.
- Backwash — Reversing the water flow through a sand or DE filter to flush out trapped debris. Cartridge filters don’t backwash — you hose them off instead.
Deep Dive
Water Chemistry Terms
| Term | Definition | Target Range |
|---|---|---|
| Free Chlorine (FC) | Active, available chlorine ready to sanitize | 1–3 ppm |
| Combined Chlorine (CC) | Chlorine that’s bonded with contaminants (chloramines). This is what smells. FC minus CC = Total Chlorine | 0–0.5 ppm (lower is better) |
| Total Chlorine (TC) | Free Chlorine + Combined Chlorine. If TC is much higher than FC, you have a chloramine problem | Should be close to FC |
| pH | Measure of water acidity (0-14 scale). 7.0 is neutral | 7.4–7.6 |
| Total Alkalinity (TA) | Measures water’s ability to resist pH changes (buffering capacity) | 80–120 ppm |
| Calcium Hardness (CH) | Amount of dissolved calcium in the water. Too low = water attacks plaster and grout. Too high = scale deposits. | 200–400 ppm |
| Cyanuric Acid (CYA) | UV stabilizer that protects chlorine from sunlight. Also called “conditioner” or “stabilizer” | 30–50 ppm |
| TDS (Total Dissolved Solids) | Everything dissolved in the water — salt, minerals, chemical residues. Rises over time | <2,000 ppm (non-salt); <6,000 ppm (salt) |
| Breakpoint Chlorination | The chlorine level needed to fully destroy all chloramines. This is what “shocking” achieves | 10x the combined chlorine level |
| Saturation Index (LSI) | Formula combining pH, TA, CH, temperature, and TDS to predict whether water is corrosive or scale-forming | -0.3 to +0.3 (balanced) |
Equipment Terms
| Term | Definition |
|---|---|
| Pump | The motor that circulates water through the entire system. The heart of the pool. See Pool Pumps Guide |
| Variable Speed Pump (VSP) | A pump that runs at adjustable RPMs. Uses dramatically less electricity than single-speed. Now standard on new pools |
| Impeller | The spinning blade inside the pump that actually moves the water. Can clog with debris |
| Strainer Basket | A mesh basket at the pump inlet that catches large debris before it reaches the impeller. Empty it weekly |
| Filter (Cartridge / Sand / DE) | Removes fine particles from water. Three types with different maintenance needs. See Pool Filters Guide |
| Salt Chlorine Generator (SCG) | Converts dissolved salt into chlorine via electrolysis. The core of a salt water pool. See Salt Chlorine Generators |
| Heater | Warms pool water using gas (natural gas or propane), electric heat pump, or solar panels. See Heaters and Heat Pumps |
| Heat Pump | Electric heater that extracts heat from outdoor air (like a reverse air conditioner). Efficient but slow. Best in warm climates |
| Suction-Side Cleaner | Automatic pool cleaner powered by the pump’s suction. Connects to the skimmer line. Budget option |
| Robotic Pool Cleaner | Self-contained electric cleaner that operates independently of the pool pump. See Robotic Pool Cleaners |
| Automation System | Centralized controller (e.g., Hayward OmniLogic, Pentair IntelliCenter) that lets you manage all pool equipment from a panel or phone app |
| Actuator Valve | A motorized valve controlled by the automation system. Switches water flow between pool and spa, or between skimmer and drain |
| Check Valve | One-way valve that prevents water from flowing backward. Common before heaters and on elevated spa returns |
Pool Structure Terms
| Term | Definition |
|---|---|
| Gunite / Shotcrete | Concrete sprayed over rebar to form the pool shell. Gunite = dry mix. Shotcrete = wet mix. Both produce the same result |
| Plaster | The interior finish applied over gunite/concrete. White plaster is the basic option; pebble and quartz finishes last longer |
| Pebble Finish (PebbleTec, Smart Pebble, etc.) | A durable interior finish that mixes small pebbles or aggregates into the plaster. Lasts 10-15+ years. Textured surface |
| Coping | The cap or edging material along the top perimeter of the pool. Usually stone (travertine, flagstone) or poured concrete |
| Decking | The hardscape surface around the pool — concrete, pavers, travertine, or spray-on coatings (cool deck, spray deck) |
| Waterline Tile | Decorative tile installed at the waterline. Prevents staining on the plaster and adds visual contrast |
| Weir | The floating flap door inside the skimmer opening. It helps maintain suction even when water level drops slightly, and prevents debris from floating back out |
| Main Drain | The drain(s) at the bottom of the pool, covered by anti-vortex grates. Pulls water from the deep end for circulation. Modern pools have dual drains for safety |
| Tanning Ledge / Baja Shelf | A shallow (6-8″) flat area, usually at the pool entry. For lounging in shallow water with chairs |
| Spillover Spa | A spa elevated above pool level with a shared wall. Water “spills over” from the spa into the pool, creating a waterfall effect |
| Equipment Pad | The concrete slab where all pool equipment (pump, filter, heater, salt cell, automation) is installed. Usually behind a fence or wall |
Maintenance Action Terms
| Term | Definition |
|---|---|
| Shocking / Superchlorination | Adding a large dose of chlorine (typically 10x the combined chlorine level) to oxidize contaminants and restore water quality |
| Backwash | Reversing water flow through a sand or DE filter to flush out debris. Not applicable to cartridge filters |
| Priming | Filling the pump housing with water before starting it. A pump that “loses prime” is running without water — shut it off immediately to avoid damage |
| Vacuuming | Cleaning debris from the pool floor — manually with a vacuum head and pole, or automatically with a robotic cleaner |
| Brushing | Using a pool brush on a pole to scrub walls, steps, and corners. Prevents algae from getting a foothold. Part of your weekly routine |
| Flocking / Flocculant | A chemical that clumps tiny particles together so they sink to the floor and can be vacuumed out. Last resort for cloudy water |
| Sequestering Agent | A chemical that binds metals (iron, copper, manganese) in the water to prevent them from depositing as stains |
| Winterizing / Closing | Preparing the pool for cold months — lowering water level, blowing out lines, adding winter chemicals, covering. See Closing Your Pool for Winter |
Pro Tip: When the pool store throws acronyms at you — FC, CC, TA, CH, CYA, TDS, LSI — don’t nod along and buy whatever they recommend. Come back to this page, understand what each number means, and then make your own call. A $40 test kit and this guide will save you hundreds in unnecessary chemicals.