Pool Water Chemistry for Beginners
Reviewed April 2026
Free chlorine (FC) and pH are the two numbers that matter most. Adjust in order: TA (total alkalinity) → pH → CYA (cyanuric acid stabilizer) → calcium → chlorine. Every other parameter supports keeping those first two in range.
Calculate chlorine doseEnter your pool volume and current FC to get estimated chlorine amounts.
Starter kit: the basics you'll actually use
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- Taylor K-2006 test kit (FAS-DPD titration, so it reads free and combined chlorine separately): Check price on Amazon →
- Pool test strips (for quick daily checks): Check price on Amazon →
- Muriatic acid (pH down)No product linked. Buy locally and read the concentration off the label — it varies a lot, and the pH calculator needs that number to give you the right dose.
- Baking soda (alkalinity up): Check price on Amazon →
The two numbers that matter most:
- Free Chlorine (FC): the sanitizer. Without it, your pool is unsafe.
- pH: controls how well chlorine works. Wrong pH = wasted chemicals.
Everything else supports these two.
The 6 Parameters
Target: 1–3 ppm (unstabilized) / 3–7 ppm (CYA 40 ppm)
What it does: Primary sanitizer. Kills bacteria, viruses, and algae.
Target: 7.2–7.8, measured with a valid test
What it does: pH affects comfort, balance and sanitation. Unstabilized HOCl percentages do not describe active chlorine in a pool containing CYA.
Target: 80–100 ppm (SWG/liquid chlorine) / 100–120 ppm (trichlor)
What it does: pH buffer. Keeps pH from swinging wildly with each chemical addition.
Target: 30–50 ppm (chlorine pool) / 60–80 ppm (SWG)
What it does: Protects chlorine from UV degradation. Without CYA, outdoor pools lose approximately 90% of FC in 2 hours of sunlight (per CDC-cited photolysis research).
Target: Select from finish/equipment requirements and saturation balance
What it does: Water's need for calcium. Soft water steals calcium from pool surfaces.
Target: Exact manufacturer/model range; see salt calculator
What it does: Electrolyte for the salt cell to generate chlorine. Only relevant for saltwater pools.
The Correct Order to Add Chemicals
Never add chemicals randomly. Each parameter affects the others. The correct order, per the ANSI pool-industry standard — with one thing that sits outside the queue.
Keep chlorine in the water the whole time. What follows is the order to CORRECT things in, not permission to leave the pool unsanitised while you work through it. Some of these steps take days — stabiliser alone takes 7 to 10 to register — and a pool holding no free chlorine for that long grows algae, which costs far more to clear than the imbalance you were fixing. Maintain your normal chlorine residual throughout and test it daily while slower adjustments settle.
- Total alkalinity (TA). Fix this first. TA stabilizes pH. Trying to fix pH when TA is off is like bailing a leaky boat.
- pH. Once TA is stable, adjust pH to 7.2–7.8.
- CYA. Add stabilizer if needed. CYA changes slowly (7–10 days to register fully).
- Calcium hardness. Adjust if needed. Raises slowly.
- Chlorine/shock. Add last, after other chemistry is balanced. Unbalanced water wastes chlorine.
Wait at least 1 hour between different chemical additions. Let the pump circulate. Retest before adding the next chemical.
The CYA/FC Relationship
This is the most misunderstood concept in residential pool chemistry. Per ANSI/APSP/ICC-11, the standard advice of "keep FC at 1–3 ppm" is only valid for pools with zero CYA (no stabilizer). In any stabilized pool, the required FC is higher.
Research from O'Brien et al. (1974) established that HOCl (the active killing form of chlorine) is partially blocked by CYA. The CDC pool-water health code codifies minimum FC requirements based on CYA level:
| CYA (ppm) | Minimum FC | Target FC |
|---|---|---|
| 0 | 1 ppm | 3 ppm |
| 30 | 2 ppm | 5 ppm |
| 50 | 4 ppm | 7 ppm |
| 70 | 5 ppm | 10 ppm |
| 80 | 6 ppm | 12 ppm |
Source: TFP CYA/Chlorine Relationship table, derived from O'Brien et al. (1974) and consistent with CDC pool-water standards. If your CYA is off target, use the CYA calculator to get the exact adjustment dose.
How Often to Test
Before swimming, measure free chlorine and pH: pH 7.2–7.8, clear water with the bottom visible, no visible algae, and FC meeting both the measured-CYA minimum and the product label’s re-entry range. CDC minimums are 1 ppm without stabilizer and 2 ppm with stabilizer; stabilized pools may need more. Test FC and pH at least twice daily and more often with heavy use. A calculated dose is not swimming clearance.
- FC and pH: At least twice daily; more often with heavy use
- TA: Monthly, or whenever pH is unstable
- CYA: Monthly, or after adding a lot of new water
- Calcium hardness: Monthly for plaster pools; less often for vinyl
- Salt (SWG): Monthly, or when the cell alarm triggers
Use a proper liquid test kit. The Taylor K-2006 is the industry standard. Test strips are acceptable for quick FC and pH checks, but not accurate enough for CYA or TA.
Frequently Asked Questions
What are the most important pool chemistry numbers?
The most important numbers are free chlorine (FC) and pH. FC is your primary sanitizer. Without it, bacteria and algae grow. pH controls how effectively FC works. Every other parameter supports these two.
How often should I test my pool water?
Test FC and pH at least twice daily, and more often with heavy use. Test TA, CYA, and calcium hardness monthly. Test more frequently after heavy use, rain, or visible problems.
In what order should I add pool chemicals?
Correct order: (1) Total alkalinity, (2) pH, (3) CYA, (4) calcium hardness, (5) chlorine/shock. Always fix TA before pH. Add one chemical at a time using its label. Retest only after that chemical’s mixing/wait interval: this site uses at least 4 hours for pH, 6 for TA, 24 for CH, 48 for salt, and 7 days for CYA; longer label instructions govern. Recalculate from each fresh reading.
What is CYA and why does it matter?
CYA (cyanuric acid) is a stabilizer that protects chlorine from UV degradation. Without CYA, outdoor pools lose 90% of their chlorine within 2 hours in full sun. More CYA requires more FC; there is no sudden chemical cliff at 80 ppm.
Why does my pool need chlorine every day?
Chlorine is consumed continuously by UV light, organic material (bather load, debris, algae), and chemical reactions. Without a stabilizer (CYA), outdoor pools lose chlorine even faster. Daily chlorine loss of 1–3 ppm is a typical rule of thumb in summer; actual loss varies with CYA level, UV exposure, and bather load.
Ready to Adjust? Pick Your Calculator
Now that you know the targets, get estimated chemical doses for your pool volume.
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