Pool Water Chemistry Chart and What Each Number Means

Pool chemistry comes down to a short list of numbers. If you know the target for each one and what it does, a test result stops being a mystery. This guide gives a target chart, explains each number in plain words, and shows where the published ranges differ.

We used CDC pages and two equipment maker manuals that we opened. Ranges differ a little between sources. That is normal. Your own equipment manual and the chemical label always come first. If you would rather have someone else handle the testing, see our weekly pool service in Grapevine.

What are the target levels for pool water?

Most home pools aim for free chlorine of 1 to 3 ppm, pH of 7.2 to 7.8, total alkalinity of 80 to 120 ppm and calcium hardness of 200 to 400 ppm. Salt pools add a salt target. The table below shows what each source says. “None” means the page we opened gives no figure.

Notes on the table:

• The CDC figures come from its home pool page and its chloramine page. CDC gives no alkalinity, hardness or stabilizer target on those pages.
• Hayward says its table summarizes levels recommended by the Association of Pool and Spa Professionals (APSP). The group is now called PHTA. We did not open the standard itself, so we cite Hayward’s manual for those numbers.
• Pentair’s salinity row applies to its IntelliChlor cell. Other cells have other ranges.

What does free chlorine do, and how much do I need?

Free chlorine is the chlorine that is still available to kill germs and algae. CDC recommends at least 1 ppm in pools. Hayward lists 1.0 to 3.0 ppm. Pentair calls 2.0 to 4.0 ppm ideal.

Chlorine is used up all the time. CDC notes that body contaminants and sunlight lower it, so you must test it regularly. In a North Texas summer, strong sun and heavy use can pull the number down fast.

Cyanuric acid changes the target. CDC says pools that use it should keep at least 2 ppm of chlorine. More on that below.

What is combined chlorine?

Combined chlorine is total chlorine minus free chlorine. It is chlorine that has already reacted with sweat, oils and other waste. These compounds are called chloramines. They cause the sharp “chlorine smell” that many people blame on too much chlorine.

CDC says most city, county and state health departments limit combined chlorine to 0.4 ppm or less. Pentair lists 0 as its target.

CDC’s fix is to superchlorinate. Close the pool to swimmers, ventilate the area, and raise free chlorine to 10 times the combined chlorine level. Then let it fall back to the normal range. CDC also notes that ultraviolet light or ozone systems can break chloramines down. See shock for how this is usually done.

What pH should a pool have?

CDC recommends pH of 7.0 to 7.8. It says that range best balances killing germs, the life of the pipes and swimmer comfort. Hayward lists 7.2 to 7.8. Pentair calls 7.4 to 7.6 ideal.

Think of pH as a dial that decides how well everything else works. If it drifts low, the water turns corrosive. If it drifts high, scale forms and chlorine loses strength. Raypak also lists pH targets for its gas heaters, and they vary by pool type: 7.3 to 7.4 for fiberglass pools and 7.6 to 7.8 for other pool types. A heater maker can have its own limits, so check your heater manual as well.

What is total alkalinity?

Total alkalinity is the water’s buffer. It resists pH swings. Hayward and Pentair both list 80 to 120 ppm. Raypak lists 120 to 150 ppm for fiberglass pools and 80 to 120 ppm for other types.

If alkalinity is too low, pH bounces around. If it is too high, pH tends to creep up and stay up. When both are off, adjust one, retest, then adjust the other. Follow the product label for each dose.

What is calcium hardness?

Calcium hardness is the amount of dissolved calcium in the water. Hayward and Pentair both list 200 to 400 ppm. Raypak lists 200 to 400 ppm for most pools and lower ranges for fiberglass pools (200 to 300 ppm) and fiberglass spas (150 to 200 ppm).

Too little calcium can make the water seek calcium from plaster and grout. Too much causes scale on tile, heaters and salt cells. Hayward warns that scale on a salt cell points to unusually high calcium. Scale is easier to see in hard water, so watch your calcium reading.

What is cyanuric acid, and why does it matter in Texas sun?

Cyanuric acid (CYA, also called stabilizer or conditioner) shields chlorine from sunlight. Without it, the sun burns off free chlorine quickly. Hayward lists 30 to 50 ppm for outdoor pools. Pentair lists 0 to 50 ppm.

More is not better. CDC says that when a pool uses cyanuric acid, you need a higher chlorine floor (at least 2 ppm). The only way to lower CYA is to dilute the water with fresh water. Hayward says the same about salt: the only way to lower it is to partly drain and refill. Because both are hard to reduce, add them in small steps and retest.

What salt level do saltwater pools need?

A salt pool needs enough salt for the cell to make chlorine. Hayward lists 2,700 to 3,400 ppm, with 3,200 ppm as the best level. It adds that a low level reduces cell output and a high level can shut the unit down. Pentair lists 3,600 ppm as ideal, within 2,600 to 4,500 ppm.

These two numbers differ because the cells differ. Use the figure in your own cell’s manual. See salt level and our saltwater vs chlorine guide for more.

What other numbers might a test show?

Some tests and manuals list extra numbers. These are the ones you may meet.

• Total dissolved solids (TDS): Total dissolved solids is everything dissolved in the water. Pentair lists 3,000 to 6,000 ppm for salt pools, including salt. Raypak says its heaters want TDS under 3,000 ppm, and up to 6,000 ppm in salt pools.
• Saturation index: The Langelier saturation index combines pH, temperature, calcium and alkalinity into one score. Hayward lists a target of -0.2 to 0.2. Pentair lists -0.3 to +0.3. Below the range means corrosive water. Above it means scale.
• Metals: Both Hayward and Pentair list 0 ppm for metals.
• Phosphates: Pentair lists 0 to 125 ppb.

How often should I test pool water?

CDC says to test chlorine and pH at least twice per day for a home pool, and more often with heavy use. It recommends a DPD test kit for the most accurate results and calls test strips an option that is less accurate.

Here is how the main tools compare.

A weekly service plan adds a regular full check. In Marina’s weekly service, water balance covers chlorine, pH, alkalinity, calcium hardness, conditioner and salt if applicable. Daily checks in between still matter in peak summer.

How do I adjust one number safely?

Change one thing at a time, wait, then retest. Follow these steps.

1. Test and write down all numbers, not only the one that looks wrong.
2. Fix the most urgent item first. Low chlorine or very high combined chlorine usually comes before small shifts in hardness.
3. Read the product label. Measure the dose from your pool volume.
4. Add the chemical as the label says, with the pump running.
5. Wait for circulation to mix it, then retest. Many labels give a wait time.
6. Recheck after a day or two before adding more.

CDC’s chemical safety page gives clear rules. Store chemicals in their original labeled containers. Keep different chemicals apart so they cannot mix. Store them below 95 degrees F. Keep protective gear and safety data sheets close. Ventilate the pump room and storage area.

Never mix chemicals. Do not guess at doses. If a number is far out of range, or if you are unsure, call a pro rather than adding more product.

Why do the ranges differ between sources?

The ranges differ because the sources have different goals. CDC sets a floor for health. Equipment makers set ranges that protect their products and keep a warranty valid. Hayward lists problems from poor water balance as a warranty exclusion in its AquaRite manual. That is a strong reason to keep your numbers in the maker’s range.

When two sources disagree, use this order:

1. The chemical product label for dose and safety.
2. Your equipment manuals for the pump, heater, cell and surface.
3. CDC for the health floor.

Next step

If you would like help keeping these numbers in range, see our weekly pool service in Grapevine or the pool maintenance services page. Call (817) 896-1120 or send a request through the contact form. Also read the pool owner’s handbook for North Texas for the full routine.