What should pool chemical levels be for pH, chlorine, alkalinity and CYA

Where the numbers come from

Most pool chemistry charts online are copies of copies. The ranges below come from the documents those charts are supposed to be based on: the CDC's Model Aquatic Health Code (MAHC), the state pool codes of California and Florida, the CDC's guidance for home pools, and the water quality fact sheets of the Pool & Hot Tub Alliance (PHTA).

They do different jobs. The MAHC, now in its 5th edition from December 2024, describes itself as voluntary guidance that health departments can adopt for public pools. State codes such as California's Title 22 and Florida's rule 64E-9.004 are the enforceable rules for public pools in those states. For backyard pools, the CDC publishes recommendations on its healthy swimming pages, and they use the same chlorine and pH floors as the public pool code.

Where the sources disagree, this guide gives the range and names each source. When you service a public pool, the code your county enforces is the one that counts.

pH: 7.0 to 7.8

The MAHC sets pool pH at 7.0 to 7.8, and Florida uses the same range. California's Title 22 is a little narrower at 7.2 to 7.8. The CDC recommends 7.0 to 7.8 for home pools and hot tubs as well.

The reason is chlorine. The CDC explains that as pH goes up, chlorine's ability to kill germs decreases, especially above 8.0. As pH falls, especially below 7.0, chlorine works better but pool and hot tub pipes are more likely to corrode. The MAHC lists pH below 6.5 or above 8.0 among the imminent health hazards that allow a health department to order a public pool closed.

A reading of 7.8 is therefore still inside every range above, but it is the top edge. A pool that reads 7.8 week after week is one small drift away from being out of range.

Free chlorine: a floor that rises with stabilizer

Every source agrees on the floor for an unstabilized pool: at least 1 ppm of free chlorine. The MAHC, the CDC's home pool guidance and California all raise that floor to 2 ppm when cyanuric acid is in the water. Florida sets 1 to 10 mg/L for conventional swimming pools and 2 to 10 mg/L for other pool types such as wading pools. Hot tubs and spas need more: the MAHC minimum for spas is 3 ppm, and the CDC recommends at least 3 ppm in hot tubs.

The ceiling is less uniform. California sets a maximum of 10 ppm for pools and spas. The MAHC says the upper limit is whatever the chlorine product label allows, and separately treats free chlorine above 10 ppm while bathers are present as an imminent health hazard.

Combined chlorine, the chloramines that cause the familiar pool smell, is the other number worth watching. The MAHC asks public pools to take action when it goes above 0.4 ppm, and California requires operators to test it often enough to keep it below 0.4 ppm.

Cyanuric acid: the cap and the ratio

Cyanuric acid, also called CYA or stabilizer, protects chlorine from sunlight, but it also slows chlorine down, which is why the chlorine floor goes up when it is present. The MAHC caps CYA at 90 ppm for all aquatic venues, and a level of 300 ppm or higher means the pool stays closed until it is fixed. California and Florida both cap CYA at 100 ppm, and Florida adds a recommended maximum of 40 mg/L for pools and a hard maximum of 40 mg/L in spa pools.

The MAHC also watches the balance between the two. A stabilized pool where the ratio of CYA to free chlorine exceeds 45 to 1 is on its list of imminent health hazards. At the 90 ppm cap, that ratio means free chlorine has to stay at 2 ppm or more. With 45 ppm of CYA the ratio alone would allow 1 ppm, but the 2 ppm floor for stabilized pools still applies.

Hot tubs are the exception. The CDC recommends not using cyanuric acid in hot tubs at all, and the MAHC bars CYA and stabilized chlorine in new or substantially altered spas and therapy pools.

Total alkalinity, calcium and salt

Total alkalinity is the buffer that keeps pH from swinging. The MAHC sets it at 60 to 180 ppm, which matches the ANSI/APSP/ICC-11 2019 standard quoted by PHTA. PHTA's alkalinity fact sheet narrows the ideal by sanitizer: 80 to 100 ppm where salt chlorine generators or calcium, lithium or sodium hypochlorite are used, because those push pH up, and 100 to 120 ppm with dichlor, trichlor, chlorine gas or bromine, which pull pH down.

In a stabilized pool, part of the alkalinity reading is cyanurate rather than carbonate. PHTA says carbonate alkalinity is often estimated by subtracting about one third of the CYA reading from total alkalinity, and gives a more exact correction factor that depends on pH. That carbonate figure is the one used for water balance calculations.

Calcium hardness has only a ceiling in the MAHC, 2,500 ppm, plus a monthly test. Salt has no single number: the MAHC says salt levels must stay in the range specified by the chlorine generator's manufacturer, tested at least weekly or as the manufacturer instructs.

Common mistakes when reading a chemistry chart

Using the 1 ppm floor in a stabilized pool. Once there is cyanuric acid in the water, every source above moves the minimum to 2 ppm.

Letting CYA creep. PHTA notes that dichlor and trichlor release cyanuric acid, so a pool fed with them keeps receiving stabilizer. The MAHC asks for weekly CYA tests when stabilized chlorine is the main disinfectant, and a test 24 hours after any CYA is added.

Trusting strips for close calls. The CDC says DPD test kits give the most accurate results and that test strips are less accurate. A strip that reads near a boundary is worth confirming.

Writing down readings without what was added. A number on its own does not explain next week's number. PoolRound logs free chlorine, pH, alkalinity, CYA and salt at each visit together with the chemicals you added, and graphs each reading per pool, so a slow climb in pH or CYA shows up across visits.

This guide summarizes published standards for general information. It is not a dosing guide or a substitute for the chemical product label, your training, or the pool code your local health department enforces. Requirements for public pools vary by state and county.

Frequently asked questions