Liquid Chlorine (10-12% Sodium Hypochlorite)
Granular Chlorine (e.g., Cal-Hypo, 65-70% available chlorine)
Chlorine Tablets (e.g., Trichlor, ~90% available chlorine)
Recommended Chlorine Addition
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Understanding Pool Chlorine and Water Chemistry
Maintaining proper chlorine levels is crucial for a safe and enjoyable swimming pool. Chlorine acts as a disinfectant, killing harmful bacteria, viruses, and algae, thus preventing waterborne illnesses and maintaining water clarity.
Why Use This Calculator?
This calculator helps pool owners determine the correct amount of chlorine to add to their pool to reach a desired Free Chlorine (FC) level. It accounts for your pool's volume, your current FC level, and the type of chlorine product you are using. Over- or under-dosing chlorine can lead to cloudy water, algae blooms, skin and eye irritation, and can even damage pool equipment and surfaces.
Key Concepts:
Parts Per Million (PPM): A measure of concentration, indicating how many parts of a substance are present for every million parts of water. In pool chemistry, it's commonly used for chlorine, pH, and other chemical levels.
Free Chlorine (FC): The active, unreacted chlorine in the water that is available to sanitize and oxidize contaminants. This is the primary measurement for disinfection effectiveness.
Total Chlorine (TC): The sum of Free Chlorine and Combined Chlorine (CC). Combined Chlorine (chloramines) are reacted chlorine compounds that are less effective disinfectants and are often responsible for the "chlorine smell" and eye irritation. Ideally, TC should be close to FC.
Shocking the Pool: A process of adding a higher dose of chlorine to break down combined chlorine, kill algae, and eliminate organic contaminants.
How the Calculation Works:
The calculator determines the amount of chlorine needed based on the difference between your target FC level and your current FC level, and the volume of your pool. The core formula to calculate the required *increase* in PPM is:
PPM Increase Needed = Target FC (PPM) - Current FC (PPM)
Once the required PPM increase is known, the amount of chlorine product needed can be calculated. The conversion factors for different chlorine types are critical:
Liquid Chlorine (10-12% Sodium Hypochlorite): Typically adds about 6-10 PPM FC per gallon per 10,000 gallons of pool water. For simplicity, we use an approximate factor. The amount of liquid chlorine needed (in fluid ounces) is approximately:
(Pool Volume in Gallons / 10,000) * PPM Increase Needed * 0.75 (approx. multiplier for liquid chlorine)
This formula estimates the fluid ounces of 10% liquid chlorine.
Granular Chlorine (e.g., Cal-Hypo): The percentage of available chlorine varies. If using 65% Cal-Hypo, it adds about 6.5 PPM FC per pound per 10,000 gallons. The amount of granular chlorine needed (in pounds) is:
(Pool Volume in Gallons / 10,000) * PPM Increase Needed / (Granular Strength % / 100)
This calculates the pounds of granular chlorine.
Chlorine Tablets (Trichlor): Trichlor tablets are potent and primarily used in floaters or feeders. They add FC but also significantly lower pH and add CYA (Cyanuric Acid). Their use is more complex, and this calculator provides an estimate for direct addition if needed. The percentage of available chlorine is typically around 90%. The amount of trichlor needed (in pounds) is:
(Pool Volume in Gallons / 10,000) * PPM Increase Needed / (Trichlor Strength % / 100)
Note: Direct addition of trichlor tablets is generally not recommended for precise FC adjustments due to its acidic nature and CYA-building properties. It's better suited for slow-release sanitation via a feeder.
You would need approximately 3.5 pounds of 65% granular chlorine.
Important Considerations:
Water Temperature & Swimmers: Higher temperatures and more swimmers increase chlorine demand.
Sunlight: UV rays break down chlorine, especially if Cyanuric Acid (CYA) levels are low.
Organic Load: Leaves, debris, and other contaminants consume chlorine.
Cyanuric Acid (CYA): Acts as a stabilizer, protecting chlorine from sunlight. Ideal CYA levels are typically 30-50 PPM for pools with chlorine, higher for salt water pools. Low CYA requires more chlorine.
pH Level: Chlorine is most effective when the pH is between 7.2 and 7.6. If pH is too high, chlorine becomes significantly less effective.
Testing: Always use a reliable pool water test kit to verify your FC, TC, and pH levels before and after adding chemicals.
Product Concentration: Always check the label of your specific chlorine product for its exact percentage of available chlorine, as this can vary by brand and type.
function calculateChlorine() {
var poolVolumeGallons = parseFloat(document.getElementById("poolVolumeGallons").value);
var targetFreeChlorinePPM = parseFloat(document.getElementById("targetFreeChlorinePPM").value);
var currentFreeChlorinePPM = parseFloat(document.getElementById("currentFreeChlorinePPM").value);
var chlorineType = document.getElementById("chlorineType").value;
var granularStrength = parseFloat(document.getElementById("granularStrength").value);
var trichlorStrength = parseFloat(document.getElementById("trichlorStrength").value);
var resultValueElement = document.getElementById("result-value");
var resultUnitElement = document.getElementById("result-unit");
var notesElement = document.getElementById("notes");
resultValueElement.innerText = "–";
resultUnitElement.innerText = "–";
notesElement.innerText = "";
if (isNaN(poolVolumeGallons) || poolVolumeGallons <= 0) {
notesElement.innerText = "Please enter a valid pool volume in gallons.";
return;
}
if (isNaN(targetFreeChlorinePPM) || targetFreeChlorinePPM < 0) {
notesElement.innerText = "Please enter a valid target Free Chlorine level.";
return;
}
if (isNaN(currentFreeChlorinePPM) || currentFreeChlorinePPM < 0) {
notesElement.innerText = "Please enter a valid current Free Chlorine level.";
return;
}
var ppmIncreaseNeeded = targetFreeChlorinePPM – currentFreeChlorinePPM;
if (ppmIncreaseNeeded <= 0) {
notesElement.innerText = "Your current Free Chlorine level is already at or above the target. No chlorine needs to be added.";
resultValueElement.innerText = "0.0";
resultUnitElement.innerText = "units";
return;
}
var amountNeeded = 0;
var unit = "";
var note = "";
if (chlorineType === "liquid") {
// Approximate factor: 0.75 fl oz of 10% liquid chlorine per 10,000 gallons raises FC by 1 PPM
amountNeeded = (poolVolumeGallons / 10000) * ppmIncreaseNeeded * 0.75;
unit = "fl oz (10% Sodium Hypochlorite)";
note = "This is an estimate for 10% liquid chlorine. Adjust based on your product's specific concentration.";
} else if (chlorineType === "granular") {
if (isNaN(granularStrength) || granularStrength 100) {
notesElement.innerText = "Please enter a valid granular chlorine strength (1-100%).";
return;
}
// Factor: 1 lb of 100% granular chlorine per 10,000 gallons raises FC by 9.6 PPM
// To raise FC by 1 PPM: (10,000 / 9.6) lbs / 10,000 gallons = 0.104 lbs per 10,000 gallons
// Amount Needed (lbs) = (Pool Volume / 10000) * PPM Increase Needed / (Granular Strength / 100)
amountNeeded = (poolVolumeGallons / 10000) * ppmIncreaseNeeded / (granularStrength / 100);
unit = "lbs (granular)";
note = "This is an estimate for " + granularStrength + "% granular chlorine (e.g., Cal-Hypo). Always check your product label.";
} else if (chlorineType === "tablets") {
if (isNaN(trichlorStrength) || trichlorStrength 100) {
notesElement.innerText = "Please enter a valid trichlor strength (1-100%).";
return;
}
// Similar calculation to granular, but assumes Trichlor concentration
amountNeeded = (poolVolumeGallons / 10000) * ppmIncreaseNeeded / (trichlorStrength / 100);
unit = "lbs (Trichlor Tablets)";
note = "Direct addition of Trichlor tablets is generally not recommended for precise FC adjustments due to its acidic nature and CYA-building properties. Best used in a feeder.";
}
if (amountNeeded > 0) {
resultValueElement.innerText = amountNeeded.toFixed(2);
resultUnitElement.innerText = unit;
notesElement.innerText = note + " Always test water after addition.";
}
}
// Show/hide specific input fields based on selected chlorine type
document.getElementById('chlorineType').onchange = function() {
var selectedType = this.value;
document.getElementById('granularStrengthGroup').style.display = (selectedType === 'granular') ? 'flex' : 'none';
document.getElementById('trichlorStrengthGroup').style.display = (selectedType === 'tablets') ? 'flex' : 'none';
if (selectedType !== 'granular' && selectedType !== 'tablets') {
document.getElementById('granularStrengthGroup').style.display = 'none';
document.getElementById('trichlorStrengthGroup').style.display = 'none';
}
};
// Initial setup for strength fields
document.addEventListener('DOMContentLoaded', function() {
document.getElementById('chlorineType').dispatchEvent(new Event('change'));
});