Pool & spa
Pool CYA Calculator
Doses cyanuric acid, the one parameter you cannot bring back down with a chemical.
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. CYA cannot be removed chemically; the only way down is dilution. It also accumulates on its own if you use stabilised tablets, which is why pools drift high over a season. High CYA does not stop chlorine working, but it slows it enough that the required chlorine level rises with it.
Get a Free Business AuditHow the calculation works
The dose to raise cyanuric acid is the gap times the volume, using stabiliser or conditioner. Cyanuric acid shields chlorine from ultraviolet light, which in sunlight is the difference between chlorine lasting hours and lasting a day, so an outdoor pool needs some. It also binds chlorine, reducing the proportion available to sanitise at any given free chlorine reading, which is why the two parameters have to be read as a pair.
What moves the number
- Current level against target, which differs for chlorine and salt pools.
- Whether the pool is outdoors in strong sun, which is the reason to have any.
- Which chlorine products are used, since some add cyanuric acid every dose.
- Volume, which scales the dose.
Where this one goes wrong
Cyanuric acid can only be reduced by diluting the water, so it is the parameter most easily ruined and hardest to fix. The common way it creeps up is through stabilised chlorine products: trichlor tablets and dichlor both add cyanuric acid with every dose, so a pool run on tablets climbs steadily until the chlorine stops working effectively, which owners experience as needing more and more chlorine. Switching to liquid chlorine or cal hypo stops the climb. Recognising that pattern is more useful than dosing around it, because the answer is partial drainage and a change of product rather than more chemicals.
Before you quote
- Remember cyanuric acid can only be lowered by dilution.
- Check which chlorine product is in use, since tablets raise it every dose.
- Read free chlorine requirements against the cyanuric acid level.
Where the rules come from
Questions
About this calculator
How do I lower cyanuric acid?
By diluting, meaning partially draining and refilling, or using a reverse osmosis treatment service. No chemical removes it. That makes it the parameter to be most careful about, since over-stabilising a pool is corrected with water rather than with another product.
Why does my cyanuric acid keep rising?
Almost certainly stabilised chlorine products. Trichlor tablets and dichlor both add cyanuric acid with every dose, so a pool run on tablets climbs steadily. Owners experience it as needing more and more chlorine for the same result. Switching to liquid chlorine or cal hypo stops the climb.
Do I need cyanuric acid at all?
An outdoor pool does, because without it sunlight destroys chlorine within hours. An indoor pool needs little or none, since there is no ultraviolet exposure, and adding it indoors only binds chlorine for no protective benefit. It is one of the clearer differences between indoor and outdoor water chemistry.
The formula
about 0.85 lb of cyanuric acid per 10,000 gallons raises CYA 10 ppm
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How to use this calculator
- Pool volume (gallons). Enter your own figure; the page starts at 20,000.
- Current CYA (ppm). Enter your own figure; the page starts at 20.
- Target CYA (ppm). Enter your own figure; the page starts at 40.
- Price per pound or gallon ($). Enter your own figure; the page starts at $3.2.
The result updates as you type, so you can try a figure, see what it does to cyanuric acid to add, 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 |
| Current CYA (ppm) | 20 |
| Target CYA (ppm) | 40 |
| Price per pound or gallon | $3.2 |
What comes out
| Result | Value |
|---|---|
| Cyanuric acid to add main result | 3.4 |
| Change needed | 20.0 |
| Estimated cost | $10.88 |
| Dose per 10,000 gallons | 1.7 |
Add about 3.4 to move 20,000 gallons from 20 to 40.
How sensitive the answer is
Holding everything else steady and changing only price per pound or gallon, this is what happens to cyanuric acid to add. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Price per pound or gallon ($) | Cyanuric acid to add |
|---|---|
| $1.6 | 3.4 |
| $2.4 | 3.4 |
| $3.2 example above | 3.4 |
| $4.8 | 3.4 |
| $6.4 | 3.4 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Pool volume (gallons)
- A number, between 0 and 2000000, starting at 20,000.
- Current CYA (ppm)
- A number, between 0 and 200, starting at 20.
- Target CYA (ppm)
- A number, between 0 and 200, starting at 40.
- Price per pound or gallon ($)
- A money amount, starting at $3.2.
What the results tell you
| Result | What it is |
|---|---|
| Cyanuric acid to add | The headline result. A decimal figure. |
| Change needed | A decimal figure. |
| Estimated cost | A money figure. |
| Dose per 10,000 gallons | A decimal figure. |
Estimating is the easy part
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