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Guide · Pool chemistry

Understanding Your Pool Water Tests

10 min readUpdated April 2026Affiliate disclosure
Summary

Start with FC and pH. Plan adjustments to TA and pH together, then CYA and calcium if needed. Keep chlorine in range as you go. CYA affects how much FC you need, and every addition needs time to mix before you retest.

Estimate a chlorine addition

Have your pool’s gallons and fresh FC and CYA results ready.

Testing and chemical supplies

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Start routine tests with FC and pH:

  1. Free Chlorine (FC): the sanitizer residual. Meet the minimum for measured CYA and the product label.
  2. pH: affects sanitation, comfort and water balance. Use a valid test.

Use CYA, TA and calcium alongside those tests, plus salt-cell requirements if you have one.

Six Pool Water Readings

FCFree Chlorine

Target: Minimum for your CYA reading, within the label’s operating and swimming limits

What it does: Chlorine remaining in the water for sanitation. You need more as CYA rises.

Too low: Keep swimmers out if FC is below the required minimum. Use a fresh reading to calculate the correction.
Too high: Keep swimmers out until FC meets the label’s re-entry range as well as the CYA minimum. Treat the routine calculator’s upper limit as a dosing limit, not a swimming cutoff.
FC Calculator →
pHpH

Target: 7.2–7.8; use a valid pH test

What it does: pH affects comfort, sanitation and water balance. For water containing CYA, use stabilized-water guidance to assess chlorine activity rather than an unstabilized HOCl percentage.

Too low: Outside the operating range, low pH can affect comfort and damage surfaces or equipment. Assess it with TA and the finish requirements.
Too high: High pH can contribute to scale or cloudiness along with the rest of the water balance. Chlorine doesn’t switch off at a particular pH. Look at those readings together when planning a correction.
pH Calculator →
TATotal Alkalinity

Target: Calculator references: 80–100 ppm for SWG/liquid chlorine; 100–120 ppm for trichlor. Assess full balance.

What it does: TA tells you how well the water buffers acid. Consider it with pH when planning adjustments.

Too low: Low buffering capacity can make pH less stable. Recheck TA and pH together before correction.
Too high: High TA can contribute to pH rise and calcium saturation. Acid reduces TA and pH; aeration can raise pH without adding TA.
TA Calculator →
CYACyanuric Acid (Stabilizer)

Target: Calculator references: 30–50 ppm for chlorine pools; 60–80 ppm for SWG. Follow the exact cell manual.

What it does: Helps protect chlorine from sunlight while changing the FC needed for sanitation.

Too low: Less sunlight protection can increase chlorine demand. Choose a CYA target for the sanitizer and equipment.
Too high: Higher CYA calls for higher FC. Review management if your required target is outside the calculator or product limits.
CYA Calculator →
CHCalcium Hardness

Target: Finish and equipment requirements, assessed with calcium saturation

What it does: Measures dissolved calcium. Assess it with pH, TA, temperature and finish requirements.

Too low: Low calcium-carbonate saturation can etch plaster. Have suspected metal corrosion assessed separately from a CH test.
Too high: High calcium-carbonate saturation can form scale or haze. Assess hardness alongside the other water-balance readings before choosing a correction.
CH Calculator →
SaltSalt (SWG only)

Target: Your exact cell model’s operating range; see its manual

What it does: Provides the salt a chlorine generator uses. The cell still needs adequate flow and appropriate operating settings.

Too low: Below the model’s range, the cell may underproduce or stop. Check the alarm and manual; maintain FC manually while resolving the problem.
Too high: Above the model’s range, follow its high-salt instructions and assess any needed water exchange before lowering the pool level.
Salt Calculator →

Making Adjustments Without Letting Chlorine Fall

Test before deciding what to add. TA and pH affect each other, and each chemical needs its own mixing and waiting period. Follow the label’s compatibility instructions.

Keep chlorine in the water the whole time. Maintain routine FC for your CYA reading while the other adjustments settle. Test FC and pH at least twice daily, more often with heavy use. If there’s algae, keep the pool closed while you follow the treatment plan and pass all completion checks.

  1. Total alkalinity (TA). Assess it with pH. The alkalinity calculator estimates a staged correction when an addition is needed.
  2. pH. Use valid pH within 7.2–7.8 and coordinate corrections with TA.
  3. CYA. Add only if below the selected target. Follow the dissolution and retesting period; do not immediately repeat the dose.
  4. Calcium hardness. Choose a target from finish and equipment requirements plus a saturation assessment.
  5. Chlorine/shock. Maintain routine FC throughout corrections. Use algae treatment only when indicated, after establishing valid pH.

Add chemicals separately as their labels direct. Before retesting, wait at least 4 hours for pH, 6 hours for TA, 24 hours for CH, 48 hours for salt and 7 days for CYA. Wait longer if the label requires it, then use the fresh result to calculate any further dose.

How CYA Changes the Chlorine Target

As CYA rises, you need more free chlorine for routine care. The calculator checks the CYA-based minimum and a conservative dosing ceiling. Before swimming, also test pH, check for algae and make sure you can see the bottom.

Use the table to see how CYA changes the calculator’s chlorine minimum. CDC guidance does not validate the example doses. CDC minimums are 1 ppm without stabilizer and 2 ppm with it, while this calculator keeps a conservative 2 ppm minimum even at zero CYA. The example targets illustrate the CYA relationship; choose your own target for your pool and product limits.

CYA (ppm)Tool minimum FCExample target FC
02 ppm3 ppm
302 ppm5 ppm
504 ppm7 ppm
705 ppm10 ppm
806 ppm12 ppmOutside routine calculator limit

Read about the residential CYA/FC reference in the methodology. The routine calculator stops dosing at targets above 10 ppm, including the 12 ppm example at CYA 80 ppm. Don’t lower your chosen target to get a dose, or use the algae-treatment tool for routine care. Have a qualified pool professional review your CYA plan against the product label and exact cell manual. Use the CYA calculator to review the adjustment or exchange guidance.

Plan Your Testing Schedule

A dose calculation cannot clear a pool for swimming. Before anyone swims, test free chlorine (FC) and pH. Keep pH at 7.2–7.8, with clear water, the bottom visible and no visible algae. FC must meet both the minimum for measured CYA and the chlorine label’s re-entry range. CDC minimums are 1 ppm without stabilizer and 2 ppm with it; a pool with CYA can require more. Test FC and pH at least twice daily, and more often during heavy use.

  • FC and pH: Test at least twice daily, and more often during heavy use
  • TA: Follow your care instructions; recheck when pH is unstable
  • CYA: Recheck after water replacement or stabilized-chlorine additions
  • Calcium hardness: Follow finish and equipment instructions; recheck when water balance changes
  • Salt (SWG): Follow the cell manual; check independently when an alarm appears

Use tests that cover the readings and concentration range you need. The Taylor K-2006 kit provides separate FC and combined-chlorine tests. Follow each method’s instructions and limitations, especially after high-chlorine treatment; never dose from an unreadable result.

Frequently Asked Questions

What are the most important pool chemistry numbers?

Start with free chlorine and a trustworthy pH test. Use CYA to set the chlorine minimum, and consider TA and calcium hardness when assessing balance. A salt cell also needs salt within its operating range. Before anyone swims, check clarity and algae as well as chemistry.

How often should I test my pool water?

Test FC and pH at least twice daily, more often during heavy use, as CDC guidance advises. Use your pool’s care instructions for the other tests, and recheck after chemical additions, water replacement or a visible problem.

In what order should I add pool chemicals?

Keep routine chlorine in range and adjust TA and pH together, adding other chemicals only when needed. Add them separately as their labels direct and let each mix. Before retesting, wait at least 4 hours for pH, 6 hours for TA, 24 hours for CH, 48 hours for salt and 7 days for CYA, or longer if the label requires it. Calculate any further addition from the fresh test.

What is CYA and why does it matter?

CYA protects chlorine from sunlight and raises the FC you need for sanitation. Test it before choosing a chlorine target or adding stabilizer. Chlorine doesn’t suddenly lock up at the calculator’s addition limit; use that limit as a point to review your CYA plan.

Why does my pool need chlorine every day?

Your chlorine demand changes with sunlight, swimmers, debris and algae. Test FC, then calculate the gap to your CYA-based target. Recalculate as conditions change instead of repeating yesterday’s dose.

Choose a Calculator From Your Test Results

Use the calculator for the adjustment your fresh tests call for. Enter the pool’s actual gallons and the strength on your product label.

Chlorine →pH →Alkalinity →CYA →Calcium →Salt →

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