This is a working reference, not a deep theory dive. The ranges below match the Pool & Hot Tub Alliance recommendations, and the corrective actions are what most established service operators do day-to-day.
The five tests, by priority
| Test | Ideal range | Why it matters |
|---|---|---|
| Free Chlorine (FC) | 1.0 – 4.0 ppm (rises with CYA) | The active sanitizer. Below 1.0 = unsafe. Above 4.0 = irritation, equipment wear. |
| pH | 7.4 – 7.6 | Out of range = chlorine becomes ineffective AND water becomes corrosive or scale-forming. |
| Total Alkalinity (TA) | 80 – 120 ppm | Buffers pH against drift. Low TA means pH bounces around constantly. |
| Cyanuric Acid (CYA) | 30 – 50 ppm (outdoor pools) | "Sunscreen" for chlorine. Below 30 = chlorine burns off in sun. Above 100 = chlorine becomes inactive. |
| Calcium Hardness (CH) | 200 – 400 ppm | Below 150 = water corrodes plaster/metal. Above 400 = scale. |
Order of operations on every visit
Test in this order, because each result affects how you read the next:
- Free Chlorine first — if zero, the pool is unsafe and you have a bigger issue than chemistry tweaks
- pH — needs to be in range before any chemistry adjustments stick
- Total Alkalinity — affects how stable your pH adjustment will be
- Cyanuric Acid — only test monthly; doesn't change much week-to-week unless you're adding stabilized chlorine (trichlor tablets contain CYA)
- Calcium Hardness — also monthly
Corrective actions — quick reference
| Problem | Add this | Approximate dose (10,000 gal pool) |
|---|---|---|
| Low pH (< 7.2) | Sodium carbonate (soda ash) — raises pH and TA | 1 lb raises pH ~0.2 |
| High pH (> 7.8) | Muriatic acid OR sodium bisulfate | 1 qt muriatic lowers pH ~0.4 |
| Low TA (< 80) | Sodium bicarbonate (baking soda) | 1.5 lb raises TA ~10 ppm |
| High TA (> 120) | Muriatic acid (lowers BOTH pH and TA — work pH back up after) | 1 qt lowers TA ~10 ppm |
| Low chlorine | Liquid chlorine (sodium hypochlorite) for fast effect, or trichlor tablets for slow | 1 gal liquid chlorine raises FC ~10 ppm |
| Low CYA | Cyanuric acid (stabilizer) — adds slowly, takes a week | 1 lb raises CYA ~13 ppm |
| Low calcium | Calcium chloride | 1 lb raises CH ~10 ppm |
The CYA + chlorine relationship — the most-misunderstood thing in pool service
"Free chlorine should be 1-4 ppm" is the textbook answer. The reality is more nuanced — CYA dramatically changes how much chlorine you need.
The rule of thumb that actually works: FC should be at least 7.5% of CYA.
| CYA | Minimum FC needed | Target FC |
|---|---|---|
| 30 ppm | 2.3 ppm | 3-5 ppm |
| 50 ppm | 3.8 ppm | 4-6 ppm |
| 80 ppm | 6.0 ppm | 7-9 ppm |
| 100+ ppm | 7.5+ ppm | Drain or partial-drain — too high to maintain |
This is why pools that test "fine" on chlorine (3 ppm) but have CYA of 90 ppm still get algae. The chlorine is being held inactive by the high CYA. The fix is partial drain to dilute CYA, not more chlorine.
When to drain instead of treating
Three scenarios where treating is throwing money away:
- CYA above 100 ppm — partial drain (33-50% of water) is the only fix. CYA doesn't degrade naturally.
- Total Dissolved Solids (TDS) above 1500 ppm above the fill water baseline — water gets cloudy and chemistry stops responding to inputs. Partial drain.
- Salt above 4500 ppm in a salt-cell pool — same idea, salt cells stop working efficiently.
The customer push-back is always "but draining wastes water." Run the math: a 33% drain on a 15,000 gal pool is 5,000 gallons. At typical water rates that's $15-30 of water. Compared to weeks of trying to fix chemistry that won't respond — and the algae outbreak that's coming if you don't — it's the cheaper option.
Field hygiene
Few things that prevent the most common chemistry mistakes:
- Always test in the deep end — surface water near returns is unrepresentative
- Refresh your test reagents quarterly — DPD-1 and DPD-3 lose potency in 90 days
- Never add muriatic acid to skimmer — eats the heater. Pour into the deep end with the pump running.
- Wait 30 minutes between adding different chemicals — chlorine + CYA-stabilized acid can release chloramine gas if mixed too closely
Daily Invoice Maker's service log captures all five readings in seconds, with color-coded warnings when any value drifts out of range. Ranges are pre-loaded — you just type the numbers. Download free to use it on your route today.
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