Pool & spa
Pool Chemical Calculator
Doses the main parameters together, which is how pool chemistry actually works.
Result
Dose against a test result, never against a schedule. Add chemicals in stages with the pump running, wait for a full turnover, then retest before adding more. Never mix chemicals, and never add water to acid. Where a product label differs from the figure here, the label wins. Work in order: alkalinity first because it buffers pH, then pH, then calcium, then stabiliser, and chlorine throughout. Adding everything at once makes it impossible to tell what worked, and some combinations react dangerously.
Get a Free Business AuditHow the calculation works
Each parameter's dose is its gap to target times the volume, converted to the product used, but the value of doing them together is the order. Chemistry is sequential rather than parallel: total alkalinity is corrected first because it buffers pH, then pH because it governs chlorine effectiveness and scaling, then calcium hardness, then stabiliser, and chlorine last once the water it is going into will let it work.
What moves the number
- Which parameters are out and by how much.
- Volume, which scales every dose.
- The order corrections are made in, which affects how much is needed.
- Fill water chemistry, which sets the pool's baseline tendencies.
Where this one goes wrong
Changing everything at once makes it impossible to tell what worked, and several of these chemicals interact, so simultaneous dosing can overshoot in ways a sequence does not. Correct one parameter, circulate, retest, then move on. The order matters because alkalinity controls pH behaviour and pH controls chlorine effectiveness, so dosing chlorine into unbalanced water wastes it. And never combine products: adding two chemicals close together in the same spot, particularly chlorine and acid, can produce toxic gas, so each goes in separately with circulation between.
Before you quote
- Correct in sequence: alkalinity, pH, hardness, stabiliser, then chlorine.
- Circulate and retest between corrections rather than dosing at once.
- Add each chemical separately, never combining them.
Where the rules come from
Questions
About this calculator
What order should pool chemicals be added in?
Total alkalinity first because it buffers pH, then pH because it governs chlorine effectiveness, then calcium hardness, then stabiliser, and chlorine last. Dosing chlorine into unbalanced water largely wastes it, which is why the sequence saves both money and effort.
Can I add several chemicals at the same time?
No, for two reasons. Chemically, some combinations are dangerous and produce toxic gas, so each goes in separately with circulation between. Practically, changing everything at once makes it impossible to tell what worked and easy to overshoot, since the parameters interact.
Why does my pool need the same corrections every week?
Usually the fill water or the chlorine product. Fill water that is high in alkalinity or hardness pushes the pool that way with every top-up, and stabilised chlorine tablets raise cyanuric acid continuously. Testing the fill water explains most recurring chemistry battles.
The formula
each dose = (target - current) x standard rate per 10,000 gallons x volume / 10,000
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How to use this calculator
- Pool volume (gallons). Enter your own figure; the page starts at 20,000.
- Free chlorine now (ppm). Enter your own figure; the page starts at 0.5.
- pH now. Enter your own figure; the page starts at 7.8.
- Total alkalinity now (ppm). Enter your own figure; the page starts at 70.
- Calcium hardness now (ppm). Enter your own figure; the page starts at 180.
- Stabiliser now (ppm). Enter your own figure; the page starts at 25.
The result updates as you type, so you can try a figure, see what it does to liquid chlorine to 3 ppm, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Pool volume (gallons) | 20,000 |
| Free chlorine now (ppm) | 0.5 |
| pH now | 7.8 |
| Total alkalinity now (ppm) | 70 |
| Calcium hardness now (ppm) | 180 |
| Stabiliser now (ppm) | 25 |
What comes out
| Result | Value |
|---|---|
| Liquid chlorine to 3 ppm main result | 53.5 |
| Muriatic acid to pH 7.5 | 48.0 |
| Bicarbonate to 100 ppm alkalinity | 9.0 |
| Calcium chloride to 250 ppm | 17.5 |
| Stabiliser to 40 ppm | 2.6 |
For 20,000 gallons: 53.5 fl oz of liquid chlorine, 48.0 fl oz of acid, 9.0 lb of bicarbonate, 17.5 lb of calcium and 2.6 lb of stabiliser. Add them one at a time, not together.
How sensitive the answer is
Holding everything else steady and changing only pool volume (gallons), this is what happens to liquid chlorine to 3 ppm. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Pool volume (gallons) | Liquid chlorine to 3 ppm |
|---|---|
| 10,000 | 26.8 |
| 15,000 | 40.1 |
| 20,000 example above | 53.5 |
| 30,000 | 80.3 |
| 40,000 | 107.0 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Pool volume (gallons)
- A number, between 0 and 2000000, starting at 20,000.
- Free chlorine now (ppm)
- A number, between 0 and 30, starting at 0.5.
- pH now
- A number, between 6 and 9, starting at 7.8.
- Total alkalinity now (ppm)
- A number, between 0 and 400, starting at 70.
- Calcium hardness now (ppm)
- A number, between 0 and 1200, starting at 180.
- Stabiliser now (ppm)
- A number, between 0 and 200, starting at 25.
What the results tell you
| Result | What it is |
|---|---|
| Liquid chlorine to 3 ppm | The headline result. A decimal figure. |
| Muriatic acid to pH 7.5 | A decimal figure. |
| Bicarbonate to 100 ppm alkalinity | A decimal figure. |
| Calcium chloride to 250 ppm | A decimal figure. |
| Stabiliser to 40 ppm | A decimal figure. |
Keep going
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