Pool Service Glossary and FAQ Hub
Reviewed for 2026, updated September 8, 2026.
Plain-language definitions of the chemistry, equipment, and route terms pool technicians use every day, plus answers to the questions we hear most often from service companies.
- Acid demand
- The amount of acid required to lower a pool's pH to the target range. It is measured with a test kit by counting drops of reagent, and it is influenced by total alkalinity, since higher alkalinity resists pH change and increases the acid needed.
- Algaecide
- A chemical product used to prevent or help control algae growth in pool water. Algaecides are a supplement to proper chlorine levels, not a replacement for them, and different formulations target different types of algae.
- Backwash
- The process of reversing water flow through a sand or DE filter to flush trapped debris out to waste. Backwashing is typically triggered by a rise in filter pressure above the clean baseline reading.
- Bather load
- The number of swimmers using a pool and how heavily they use it over a period of time. Higher bather load introduces sweat, sunscreen, and other organic waste that consumes sanitizer and raises chlorine demand.
- Breakpoint chlorination
- The point at which enough chlorine has been added to oxidize all combined chlorine and organic contaminants, after which additional chlorine remains as free chlorine. Reaching breakpoint is the goal of a proper shock treatment.
- Calcium hardness
- A measure of dissolved calcium in the water, expressed in parts per million. Water that is too low in calcium can etch plaster and corrode equipment, while water that is too high tends to form scale on surfaces and inside heaters.
- Cartridge filter
- A pool filter that traps debris in a pleated fabric element which is removed and rinsed by hand rather than backwashed. Cartridge filters are common on residential pools and their cleaning interval depends on debris load and pool size.
- Chlorine demand
- The amount of chlorine consumed by contaminants in the water before any free chlorine remains available to sanitize. A pool with high chlorine demand, such as one with algae or heavy organic load, will show low free chlorine no matter how much is added until that demand is met.
- Clarifier
- A product that causes fine suspended particles to clump together so the filter can capture them more easily. Clarifiers help clear mildly cloudy water but only work if the filter and pump are functioning properly.
- Combined chlorine
- Chlorine that has bonded with nitrogen compounds from sweat, urine, and other contaminants, forming chloramines. Combined chlorine is a poor sanitizer and is the source of the sharp chlorine smell and eye irritation swimmers complain about. It is calculated as total chlorine minus free chlorine.
- Cyanuric acid
- Also called stabilizer or conditioner, cyanuric acid protects chlorine from being broken down by ultraviolet light. Too little allows rapid chlorine loss in sunlight, while too much reduces chlorine effectiveness and requires higher free chlorine levels to compensate.
- DE filter
- A filter that uses diatomaceous earth powder coated on internal grids to trap very fine particles. DE filters provide the finest filtration of the common types and are backwashed periodically, after which fresh DE is added.
- Dichlor
- A granular, stabilized form of chlorine that dissolves quickly and is often used for shocking. Because it contains cyanuric acid, repeated use raises the stabilizer level in the pool over time.
- Flocculant
- A product that binds suspended particles into heavier clumps that sink to the floor, where they are removed by vacuuming to waste. Flocculant is a stronger intervention than clarifier and is typically used for severely cloudy water.
- Free chlorine
- The portion of chlorine in the water that is available to sanitize and oxidize contaminants. Free chlorine is the primary reading a technician checks at every stop, and the appropriate level depends on the pool's cyanuric acid concentration.
- Langelier Saturation Index
- A calculated value, often abbreviated LSI, that combines pH, temperature, calcium hardness, total alkalinity, and total dissolved solids to predict whether water is likely to scale, etch, or remain balanced. Many technicians use an LSI calculator to fine-tune balance rather than treating each parameter in isolation.
- Muriatic acid
- A diluted form of hydrochloric acid used to lower pH and total alkalinity in pool water. It is inexpensive and effective but must be handled with protective equipment and stored away from chlorine products on the truck.
- pH
- A measure of how acidic or basic the water is. Pool water is commonly kept slightly above neutral, in a range that keeps chlorine effective, protects surfaces and equipment, and is comfortable for swimmers. pH tends to drift upward in many pools and is corrected with acid.
- Phosphates
- Nutrients that enter pool water from fertilizer runoff, leaves, some source water, and certain chemical products. Phosphates feed algae, so elevated levels can make it harder to maintain free chlorine, and phosphate removers are sometimes used on problem pools.
- Pool volume
- The estimated number of gallons a pool holds, calculated from its dimensions and average depth. Accurate volume is essential because every chemical dose is based on it, and an estimate that is far off leads to consistent under-dosing or over-dosing.
- Route density
- How many service stops are clustered within a given area or drive distance. High route density means less drive time between pools and more billable stops per day, which is the primary driver of profitability in pool service.
- Salt chlorine generator
- Equipment that produces chlorine on site by passing mildly salted pool water through an electrolytic cell. Salt pools still require chemical balancing, and the cell needs periodic inspection and cleaning to remove scale buildup.
- Sand filter
- A filter that traps debris as water passes through a bed of specially graded sand. Sand filters are cleaned by backwashing and are known for simple operation, though they capture coarser particles than DE or cartridge filters.
- Shock
- The practice of adding a large dose of chlorine or a non-chlorine oxidizer to destroy contaminants, combined chlorine, and algae. Shocking is a targeted treatment after heavy use, storms, or algae problems rather than a routine weekly step.
- Soda ash
- Sodium carbonate, a product used to raise pH in pool water. It also raises total alkalinity somewhat, so technicians account for that when balancing both parameters.
- Sodium bicarbonate
- Baking soda, used to raise total alkalinity with only a modest effect on pH. It is one of the most commonly carried balancing chemicals on a service truck.
- Total alkalinity
- A measure of the water's ability to resist changes in pH, expressed in parts per million. Adequate alkalinity keeps pH stable between visits, while low alkalinity causes pH to swing and high alkalinity makes pH difficult to lower.
- Trichlor
- A slow-dissolving, stabilized form of chlorine commonly sold as tablets for use in floaters and inline feeders. Trichlor is acidic and contains cyanuric acid, so long-term use tends to lower pH and raise stabilizer levels.
- Turnover rate
- The time it takes for the pump and filter to circulate a volume of water equal to the entire pool. Adequate daily turnover is necessary for filtration and chemical distribution, and a pump schedule that is too short is a common cause of cloudy water and low chlorine.
Questions people ask
What should a pool technician test at every weekly stop?
At a minimum, free chlorine, pH, and total alkalinity, because those three change the most week to week and determine what you dose. Combined chlorine is worth checking when the water smells strongly or swimmers complain. Calcium hardness and cyanuric acid change slowly, so most technicians test them on a monthly or seasonal schedule and after any major water addition.
Why does a pool need cyanuric acid if it already has chlorine?
Chlorine without stabilizer is destroyed quickly by sunlight, so an outdoor pool can lose most of its free chlorine in a single sunny afternoon. Cyanuric acid shields chlorine from ultraviolet light so it lasts between visits. The tradeoff is that too much stabilizer slows chlorine down, which is why technicians keep it in a moderate range and watch it rise when using stabilized products.
How do you estimate the volume of a pool you have never serviced before?
Measure the length and width, estimate the average depth by averaging the shallow and deep ends, multiply those together, and then multiply by the standard conversion factor for the shape, which is different for rectangles, ovals, and freeform pools. Record the result in the pool's file so every future dose is calculated against the same number. If the customer has original build documents, use those instead.
Is it safe to store muriatic acid and liquid chlorine on the same truck?
Only if they are kept physically separated in their own containment, with no possibility of a spill from one reaching the other. Mixing acid and chlorine produces chlorine gas, which is dangerous in an enclosed cargo area. Separate bins, secondary containment, ventilation, and protective equipment are the minimum, and quantities above certain thresholds may bring additional transport requirements.
How long does it take to clear a green pool?
It depends on how severe the algae is, the stabilizer level, the filter type, and how consistently chlorine is held high during treatment. Mild green pools often clear in a few days with high chlorine, continuous filtration, and frequent filter cleaning. Severe cases with heavy debris or very high cyanuric acid can take considerably longer and sometimes require a partial drain.
Why does pool water turn cloudy after shocking?
Shocking kills algae and oxidizes contaminants, and the dead material stays suspended until the filter removes it. Cloudiness after a shock is common and usually clears with continuous pump operation and filter cleaning. Persistent cloudiness points to a filter problem, insufficient run time, or a pH and calcium combination that is causing scale to precipitate.
How many pools can one technician service in a day?
It varies widely with route density, pool size, equipment condition, and how much cleaning each stop needs. Dense residential routes with well maintained pools allow many more stops than spread-out routes with large or heavily used pools. The useful measure is revenue per hour on the road rather than a raw stop count, because a tight route of moderately priced pools often beats a scattered route of higher priced ones.
What is the difference between a service report and a chemical log?
A chemical log is the technician's internal record of readings, doses, and observations at each visit, kept for trend analysis and liability. A service report is a customer-facing summary of what was done, usually sent after the visit. Good software generates the report from the log automatically so the technician only enters information once.
Should every pool on the route be shocked every week?
No. Routine weekly shocking wastes chemical, can drive stabilizer up when stabilized products are used, and keeps customers out of the water unnecessarily. Shock when there is a reason: elevated combined chlorine, heavy bather load, storm debris, visible algae, or free chlorine that repeatedly fails to hold. Consistent weekly balancing prevents most of the situations that would otherwise require a shock.
How should a pool company handle rain days and skipped visits?
Decide the policy in advance and tell customers before it matters. Many companies still visit in light rain because chemistry needs attention, and skip only in severe weather. Skipped stops should be logged as skipped, with the reason, and either rescheduled or credited according to the service agreement. Software that tracks skips per account keeps this fair and prevents disputes.
What records should be kept when taking over a pool from another company?
Photograph the pool and equipment pad on the first visit, record every piece of equipment with model information where visible, test the full chemistry panel including calcium hardness and cyanuric acid, and note any existing damage or problems. This baseline protects you from being blamed for conditions that predate your service and gives you a starting point for balancing.
When is it time to hire a second technician?
The common signals are stops that regularly run past daylight, new customers waiting weeks for a start date, and the owner having no time for repairs, quoting, or administration. Before hiring, shape the route so it can be split along a geographic line and standardize the logging procedure, so the new technician can take over a clean, documented section of the route rather than a tangled one.