How to use it
- Test the water. You need free chlorine, pH, total alkalinity, calcium hardness and stabilizer (CYA). A drop-based kit is more accurate than strips for alkalinity, calcium and CYA.
- Enter the volume, your readings and the products you use.
- Add the chemicals in the order shown, one at a time, with the pump running.
Why the order matters
Pool chemicals affect each other. Adding them in the wrong order means one dose undoes another, and you end up chasing readings for days.
- Total alkalinity first. It’s the buffer that decides how far pH moves. Raising it with baking soda also nudges pH up a little, which the next step accounts for.
- pH next. With alkalinity settled, the acid or soda ash dose is predictable.
- Calcium hardness. It changes slowly and barely touches pH.
- Stabilizer (CYA). It takes days to dissolve and register, so get it started early.
- Chlorine last. The right free chlorine level depends on your CYA, and chlorine works best once pH is in range.
Here’s why alkalinity comes before pH. The same pH change needs more acid when alkalinity is high, because the buffer soaks up acid before the pH moves:
Muriatic acid to lower pH from 7.8 to 7.5 in 15,000 gallons
Show the numbers
| Total alkalinity | Muriatic acid |
|---|---|
| 60 ppm | 9 fl oz |
| 80 ppm | 12 fl oz |
| 100 ppm | 14 fl oz |
| 120 ppm | 16 fl oz |
| 140 ppm | 19 fl oz |
| 160 ppm | 21 fl oz |
The targets it aims for
| Reading | Target |
|---|---|
| Total alkalinity | 80 to 120 ppm |
| pH | 7.5 (within 7.4 to 7.6) |
| Calcium hardness | 200 to 400 ppm for plaster, 150 to 250 ppm for vinyl and fiberglass |
| Stabilizer (CYA) | 40 ppm when below 30 |
| Free chlorine | The target for your CYA from the Trouble Free Pool FC/CYA chart |
These are typical for an outdoor home pool. If your salt cell manual or pool builder gives different numbers, follow theirs. The ranges fit inside the CDC’s limits for pH and the Model Aquatic Health Code’s limits for alkalinity, calcium and CYA. The pool chemistry chart explains each one.
Worked example
15,000 gallons: FC 1, pH 7.9, TA 70, CH 180, CYA 20, plaster
- Raise total alkalinity (70 → 90 ppm): 4.2 lb of baking soda (sodium bicarbonate)
- Lower pH (8.0 → 7.5): 16 fl oz of muriatic acid (31.45%)
- Raise calcium hardness (180 → 250 ppm): 12.6 lb of calcium chloride (77%, flake)
- Raise stabilizer (CYA) (20 → 40 ppm): 2.53 lb of cyanuric acid (stabilizer)
- Raise free chlorine (1 → 5 ppm): 61 fl oz of liquid chlorine (12.5%)
Then hold chlorine near 5 ppm (never below 3).
Notice the pH step. Raising alkalinity with baking soda lifts pH slightly, so the calculator works out the acid dose from the pH you’ll have after step 1, not the one you started with.
Timing between chemicals
- Wait at least 30 minutes between products with the pump running. A full turnover, usually 6 to 8 hours, is better before you retest.
- Stabilizer can take a week to fully dissolve and show up on a test. Don’t add more before then.
- Retest after each big change. Test kits and product strengths both have error, and it’s easier to add a little more than to take some out.
Never mix pool chemicals. Add each one to the pool separately. Acid and chlorine together release chlorine gas. Different chlorine products can react violently with each other. Always add chemicals to water, never water to chemicals.
What this calculator doesn’t cover
It doesn’t treat metals, phosphates or combined chlorine. If total chlorine is more than about 0.5 ppm above free chlorine, use the shock calculator to clear the combined chlorine. For a deeper check on whether your water will etch or scale, run the numbers through the LSI calculator.
Frequently asked questions
What order should I add pool chemicals?
Total alkalinity, then pH, then calcium hardness, then stabilizer, then chlorine. Alkalinity controls how much pH moves, and chlorine goes last because its target depends on stabilizer and its strength depends on pH.
How long should I wait between adding pool chemicals?
At least 30 minutes with the pump running, and ideally a full turnover of 6 to 8 hours before you retest and add the next one.
Can I add chlorine and acid at the same time?
No. Add them separately, ideally hours apart, and never pour them into the same bucket or into the skimmer together. Mixing them can release chlorine gas.
Should I raise alkalinity or lower pH first?
Fix alkalinity first. With alkalinity in range, pH is easier to set and stays put.
When can I swim after adding chemicals?
Follow the product label. As a rule, wait until the chemicals have circulated and free chlorine and pH are back in range, usually after a few hours with the pump running.
Why are my numbers different from the pool store’s?
Stores use different target ranges and often assume different product strengths. This calculator shows its targets and its working, so you can see exactly where any difference comes from.
Sources
- Home Pool and Hot Tub Water Treatment and Testing. U.S. Centers for Disease Control and Prevention (CDC), reviewed May 10, 2024.
- Model Aquatic Health Code, 5th edition (2024). CDC.
- Understanding the Chlorine/CYA Chart. Trouble Free Pool.
- Cyanuric Acid (fact sheet 6). Oregon Health Authority.
Reviewed November 7, 2026. We check the formulas against the sources above and re-run the worked examples whenever we update this page. Found something wrong? Tell us.