How much chlorine to add to your pool
Updated:
Your chlorine target is not a fixed number. It scales with your stabilizer (CYA). Enter your current free chlorine, your CYA, and your pool volume to get the exact amount of chlorine to add.
How much chlorine does my pool need?
The CDC sets the floor for home pools: at least 1 ppm of free chlorine with no stabilizer, and at least 2 ppm if you use cyanuric acid (CYA) or products that contain it, such as trichlor and dichlor. Above that floor, CYA decides how much you need. It holds most of the chlorine in a bound form, and the MAHC Annex explains that keeping CYA below a maximum ratio to free chlorine is what keeps enough active hypochlorous acid in the water. Trouble Free Pool’s chart turns that ratio into numbers: a minimum of 7.5% of your CYA and a target of about 11.5%. At CYA 40 that means a minimum of 3 ppm and a target of 5–7 ppm.
How much liquid chlorine per 10,000 gallons?
One gallon of 12.5% liquid chlorine raises 10,000 gallons by about 12.5 ppm, so a quart raises it about 3 ppm. Household bleach at 8.25% takes about 14 fl oz for each 1 ppm in 10,000 gallons, against 10 fl oz of 12.5% liquid chlorine. The calculator scales this to your exact volume, target, and product.
Liquid chlorine, cal-hypo, dichlor or trichlor?
Liquid chlorine adds nothing but chlorine and salt, which makes it the routine workhorse. Cal-hypo is granular and strong but adds calcium every time. Dichlor and trichlor tablets add cyanuric acid with every dose, so they quietly raise your CYA, and therefore your chlorine target, all season. If your CYA keeps climbing, your tablets are the reason.
How the dose is calculated
The calculator works in grams of available chlorine, then converts that to the product you picked.
Chlorine needed
grams = 0.00378541 × (target FC − current FC) × gallons
One ppm is one milligram per liter, and NIST defines the US gallon as 3.785412 liters. Each ppm in each gallon therefore takes 3.785 mg, or 0.00378541 g.
Converting to your product
liters = grams ÷ grams per liter · dry weight = grams ÷ strength
The calculator counts 125 g of available chlorine per liter of 12.5% liquid chlorine, 100 g for 10%, and 90.2 g for 8.25% household bleach. Cal-hypo (73% or 65%) and dichlor (56%) are divided by their strength.
Worked example
0.00378541 × 1 × 10,000 = 37.9 g; 37.9 ÷ 125 = 0.30 L ≈ 10 fl oz
That is the 10 fl oz of 12.5% liquid chlorine per ppm per 10,000 gallons used throughout this site.
What dichlor adds
CYA added ≈ 0.9 × chlorine added
Each molecule of dichlor releases two units of available chlorine (2 × 70.9 g) and one of cyanuric acid (129.07 g). By weight that is about 0.9 ppm of CYA for each 1 ppm of chlorine, and the calculator reports it next to the dose.
Ideal ranges
| Level | Target | Notes |
|---|---|---|
| No CYA | 1 ppm or more | CDC minimum for pools; the app aims for 2–4 ppm, from the Pentair manual. 3 ppm or more in hot tubs |
| CYA 20 | Minimum 2, target 3–5 ppm | |
| CYA 30 | Minimum 2, target 4–6 ppm | |
| CYA 40 | Minimum 3, target 5–7 ppm | |
| CYA 50 | Minimum 4, target 6–8 ppm | |
| CYA 60 | Minimum 5, target 7–9 ppm | |
| CYA 70 | Minimum 5, target 8–10 ppm | |
| CYA 80 | Minimum 6, target 9–11 ppm | TFP allows salt cells a 5% minimum |
| CYA 90 | Minimum 7, target 10–12 ppm | The MAHC maximum CYA for public pools |
Frequently asked questions
How much chlorine do I add to a 10,000 gallon pool?
To raise free chlorine by 1 ppm in 10,000 gallons takes about 10 fl oz of 12.5% liquid chlorine, or about 1.8 oz by weight of 73% cal-hypo. Multiply by however many ppm you need. Enter your real volume above for the exact amount.
How long after adding chlorine can I swim?
Check the product label first. It sets the level you can swim at, and the MAHC requires public pools to stay within label limits (5.7.3.1.1.5). Give the dose time to circulate, then test before anyone gets in. The CDC notes that readings above 10 ppm can bleach a DPD test and show a false low, so after a large dose use a test that reads that high.
Why does my chlorine disappear every day?
Either there is no stabilizer, so sunlight burns it off, or something in the water is consuming it, usually early algae. Check CYA first. Then run Trouble Free Pool’s overnight test: measure free chlorine after sunset and again before sunrise. Losing more than 1 ppm overnight means something in the water needs a shock.
Can I add chlorine and acid at the same time?
No. Never mix them or add them together, concentrated chlorine and acid produce toxic chlorine gas. Add one, let it circulate, then add the other.
Sources
- CDC, Home Pool and Hot Tub Water Treatment and Testing (May 10, 2024). Minimum free chlorine for pools and hot tubs; DPD tests bleach above 10 ppm
- CDC, Model Aquatic Health Code, 5th edition (2024), Code Language. Sections 5.7.3.1.1.2 and 5.7.3.1.1.5 (free chlorine) and 5.7.3.1.3.2 (CYA)
- CDC, Model Aquatic Health Code, 5th edition (2024), Annex. Section 5.7.3.1.3.1: how CYA binds chlorine and why the minimum rises with it
- Trouble Free Pool, CYA Chlorine Relationship (Chlorine/CYA chart). Minimum and target free chlorine by CYA
- Trouble Free Pool, Perform the Overnight FC Loss Test (OCLT). The overnight chlorine loss test
- Pentair, IntelliChlor IC15/IC20/IC40/IC60 Installation and User’s Guide (P/N 520589 Rev. R, 2023). Free chlorine 2.0–4.0 ppm
- NIST Special Publication 811, Appendix B.8: conversion factors. Liters per US gallon
Related calculators & guides
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