Glossary
Plain-language definitions of the terms used across Clear Water Dose.
- Available chlorine
- The amount of chlorine a product can deliver, given on the label as a percentage. Used to calculate doses.
- Bromine
- An alternative sanitizer, mainly for hot tubs. CDC lists 4 to 8 ppm for hot tubs. Read more
- Cal-hypo
- Calcium hypochlorite, a dry unstabilized chlorine (often 65% to 73%). Adds calcium hardness with each dose.
- Calcium hardness (CH)
- Dissolved calcium, measured as ppm of calcium carbonate. Matters most for plaster surfaces and heaters.
- Combined chlorine (CC)
- Chlorine that has reacted with ammonia-type contaminants (chloramines). Calculated as total chlorine minus free chlorine. Responsible for the "chlorine smell".
- Cyanuric acid (CYA)
- Also called stabilizer or conditioner. Protects chlorine from sunlight by binding it in reserve, which raises the free chlorine level you need. CDC recommends not using it in hot tubs. Read more
- Dichlor
- Sodium dichloroisocyanurate, a fast-dissolving stabilized chlorine granule (often 56%). Adds about 0.9 ppm CYA per 1 ppm free chlorine.
- DPD
- N,N-diethyl-p-phenylenediamine, the reagent in most chlorine tests. Turns pink in the presence of chlorine. CDC recommends DPD kits. Read more
- FAS-DPD
- A drop-count (titration) chlorine test that measures free and combined chlorine in small steps without bleaching at high levels.
- Free chlorine (FC)
- The chlorine available to disinfect, including the part held in reserve by cyanuric acid. The main number you dose to. Read more
- Muriatic acid
- Hydrochloric acid, used to lower pH and total alkalinity. Commonly 31.45% or a diluted 14.5%.
- pH
- How acidic or basic the water is. CDC recommends 7.0 to 7.8 for pools and hot tubs.
- ppm
- Parts per million. In pool water, the same as milligrams per litre (mg/L).
- Shock
- A large dose of oxidizer or chlorine used to clear contaminants or algae. With stabilizer present, the needed level rises with CYA.
- Total alkalinity (TA)
- The water's buffering capacity, measured as ppm of calcium carbonate. Controls how easily pH moves. Read more
- Total chlorine (TC)
- Free chlorine plus combined chlorine.
- Trade percent
- The strength of liquid chlorine expressed as grams of available chlorine per 100 mL. A 10% product has 10 g per 100 mL.
- Trichlor
- Trichloroisocyanuric acid, a slow-dissolving stabilized chlorine, usually tablets (about 90%). Adds about 0.6 ppm CYA per 1 ppm free chlorine and lowers pH.