Maintaining balanced pool chemistry is crucial for swimmer safety, bather comfort, and protecting your pool equipment from damage. The key parameters that most pool owners need to monitor are Free Chlorine (FC), Combined Chlorine (CC), pH, and Cyanuric Acid (CYA).
Free Chlorine (FC)
Free Chlorine is the active form of chlorine that sanitizes your pool by killing algae, bacteria, and other contaminants. Maintaining an adequate FC level (typically 1-4 ppm) is the primary defense against a green or unhealthy pool. The Free Chlorine to Combined Chlorine ratio (FC:CC) is also important; a ratio of 5:1 or higher is generally ideal. Low FC means your sanitizer isn't working effectively.
Combined Chlorine (CC)
Combined Chlorine (also known as chloramines) is formed when Free Chlorine reacts with contaminants like ammonia and nitrogen compounds. CC is less effective at sanitizing and can cause the strong "chlorine" smell many people associate with pools, as well as eye irritation. The goal is to keep CC levels very low, ideally 0.5 ppm or less. High CC levels indicate that your pool needs to be "shocked" to break down these compounds.
pH
pH measures the acidity or alkalinity of your pool water on a scale of 0 to 14. A pH of 7.0 is neutral. For swimming pools, the ideal pH range is typically 7.2 to 7.6. Maintaining pH within this range ensures that chlorine is most effective as a sanitizer. If pH is too high, chlorine becomes less effective and can lead to scaling. If pH is too low, it can be corrosive to pool equipment and irritating to swimmers.
Cyanuric Acid (CYA)
Cyanuric Acid, often called a "stabilizer" or "conditioner," protects Free Chlorine from being degraded by the sun's ultraviolet (UV) rays. While this is beneficial, CYA levels that are too high can also reduce chlorine's effectiveness. The recommended CYA range is typically 30-50 ppm for pools using stabilized chlorine or dichlor, and slightly higher (50-80 ppm) if using unstabilized chlorine and CYA is added separately. Note that CYA cannot be lowered by chemical means; the only way to reduce it is by draining and refilling a portion of the pool water.
How the Calculator Works
This calculator helps you determine the amount of pool chemicals needed to adjust your water chemistry. It focuses on the most common adjustments:
Increasing Free Chlorine: It calculates the amount of liquid chlorine (like Sodium Hypochlorite) or granular chlorine (like Calcium Hypochlorite) needed to reach your target FC from your current FC.
Reducing Combined Chlorine: If your CC is higher than your desired level, the calculator will suggest shocking your pool, which involves raising FC significantly to break down CC.
Adjusting pH: It suggests the amount of pH increaser (like Soda Ash) or pH decreaser (like Muriatic Acid or Dry Acid) needed to bring your pH into the target range.
Adjusting CYA: It estimates the amount of CYA (like Stabilizer/Conditioner) needed to reach your target CYA from your current CYA.
Formulas Used (Approximate – Chemical formulations vary):
To Increase Free Chlorine (using Liquid Chlorine – 10% Sodium Hypochlorite): Gallons Liquid Chlorine = (Target FC - Current FC) * Pool Volume Gallons * 0.000125 (Note: Adjust the multiplier (0.000125) based on the actual concentration of your liquid chlorine product, e.g., 0.000104 for 12.5% NSF, 0.000167 for 8%)
To Increase Free Chlorine (using Granular Chlorine – 65% Calcium Hypochlorite): Ounces Granular Chlorine = (Target FC - Current FC) * Pool Volume Gallons * 0.000136 (Note: Adjust the multiplier based on the actual percentage of available chlorine in your granular product, e.g., 0.000128 for 68%, 0.000136 for 65%, 0.000144 for 62%)
Shocking for High CC:
Target FC for shock is typically 10 ppm or higher, depending on CC levels. Calculate FC increase as above.
To Lower pH (using Muriatic Acid – 31.45%): Fluid Ounces Muriatic Acid = (Current pH - Target pH) * Pool Volume Gallons * 2.5 (Note: This is a general guideline. Actual amounts vary greatly by water alkalinity. Start with half the calculated amount and retest.)
To Raise pH (using Soda Ash – Sodium Carbonate): Ounces Soda Ash = (Target pH - Current pH) * Pool Volume Gallons * 1.7 (Note: This is a general guideline. Actual amounts vary greatly by water alkalinity. Start with half the calculated amount and retest.)
To Raise CYA (using Stabilizer/Conditioner – Trichloroisocyanuric Acid or Sodium Dichlor): Ounces Granular CYA Product = (Target CYA - Current CYA) * Pool Volume Gallons * 0.0075 (Note: This multiplier assumes a product that is ~56% CYA content like Dichlor. If using pure Cyanuric Acid (100% CYA), use ~0.0043. Always check your product label.)
Disclaimer: Chemical dosages are approximate and can vary based on specific product concentrations, water conditions (like alkalinity and temperature), and pool usage. Always read and follow the instructions on your chemical product labels. It's recommended to test your water frequently and make adjustments gradually, retesting after each addition.
function calculatePoolChemistry() {
var poolVolume = parseFloat(document.getElementById("poolVolume").value);
var currentFC = parseFloat(document.getElementById("currentFC").value);
var targetFC = parseFloat(document.getElementById("targetFC").value);
var currentCC = parseFloat(document.getElementById("currentCC").value);
var desiredCC = parseFloat(document.getElementById("desiredCC").value);
var currentpH = parseFloat(document.getElementById("currentpH").value);
var targetpH = parseFloat(document.getElementById("targetpH").value);
var currentCYA = parseFloat(document.getElementById("currentCYA").value);
var targetCYA = parseFloat(document.getElementById("targetCYA").value);
var resultsHtml = "
Calculated Adjustments:
";
var hasResults = false;
// Input validation
if (isNaN(poolVolume) || poolVolume currentFC) {
var fcDifference = targetFC – currentFC;
// Basic formula for liquid chlorine (10% NaOCl)
// Gallons = (Target FC – Current FC) * Pool Volume * (1 / 75000) — where 75000 is approx oz/gal * 10% concentration
// A more common multiplier derived is 0.000125 for 10% NaOCl per gallon
var liquidChlorineNeeded = fcDifference * poolVolume * 0.000125;
resultsHtml += "To raise Free Chlorine by " + fcDifference.toFixed(1) + " ppm (to " + targetFC.toFixed(1) + " ppm): Add approximately " + liquidChlorineNeeded.toFixed(2) + " gallons of 10% Liquid Chlorine.";
hasResults = true;
}
// Combined Chlorine Check (Suggest Shocking)
if (!isNaN(currentCC) && !isNaN(desiredCC) && currentCC > desiredCC && currentCC > 0.5) {
resultsHtml += "High Combined Chlorine detected (" + currentCC.toFixed(1) + " ppm). Your Free Chlorine may be depleted. Consider 'shocking' the pool by raising Free Chlorine to at least 10 ppm or higher.";
// Suggesting a shock level, calculate based on difference to 10ppm
if (!isNaN(currentFC) && currentFC < 10) {
var shockFCneeded = 10 – currentFC;
var liquidChlorineShock = shockFCneeded * poolVolume * 0.000125;
resultsHtml += "To shock to 10 ppm FC: Add approximately " + liquidChlorineShock.toFixed(2) + " gallons of 10% Liquid Chlorine.";
}
hasResults = true;
}
// pH Adjustment
if (!isNaN(currentpH) && !isNaN(targetpH)) {
if (targetpH < currentpH) {
// Using Muriatic Acid (approx. 31.45%) guideline: Fl Oz = (Current pH – Target pH) * Gallons * 2.5
var phDifference = currentpH – targetpH;
var muriaticAcidNeeded = phDifference * poolVolume * 2.5;
resultsHtml += "To lower pH from " + currentpH.toFixed(2) + " to " + targetpH.toFixed(2) + ": Add approximately " + muriaticAcidNeeded.toFixed(2) + " fluid ounces of Muriatic Acid (31.45%). Start with half and retest.";
hasResults = true;
} else if (targetpH > currentpH) {
// Using Soda Ash (Sodium Carbonate) guideline: Oz = (Target pH – Current pH) * Gallons * 1.7
var phDifference = targetpH – currentpH;
var sodaAshNeeded = phDifference * poolVolume * 1.7;
resultsHtml += "To raise pH from " + currentpH.toFixed(2) + " to " + targetpH.toFixed(2) + ": Add approximately " + sodaAshNeeded.toFixed(2) + " ounces of Soda Ash. Start with half and retest.";
hasResults = true;
}
}
// CYA Adjustment (using a typical stabilizer product calculation)
// Formula for Ounces of product to add = (Target CYA – Current CYA) * Pool Volume Gallons * 0.0075 (for ~56% CYA product)
if (!isNaN(currentCYA) && !isNaN(targetCYA) && targetCYA > currentCYA) {
var cyaDifference = targetCYA – currentCYA;
// Assuming a common Dichlor-based product which adds about 0.0075 oz/gal per 1 ppm CYA
var cyaProductNeededOz = cyaDifference * poolVolume * 0.0075;
resultsHtml += "To raise CYA from " + currentCYA.toFixed(0) + " ppm to " + targetCYA.toFixed(0) + " ppm: Add approximately " + cyaProductNeededOz.toFixed(1) + " ounces of CYA product (e.g., Dichlor, stabilizer).";
hasResults = true;
} else if (!isNaN(currentCYA) && !isNaN(targetCYA) && targetCYA < currentCYA) {
resultsHtml += "Note: Cyanuric Acid (CYA) can only be lowered by partially draining and refilling your pool.";
}
}
if (!hasResults || (isNaN(poolVolume) || poolVolume <= 0)) {
document.getElementById("result").innerHTML = "
Calculated Adjustments:
Please enter valid pool parameters to see calculations.";
} else {
document.getElementById("result").innerHTML = resultsHtml;
}
}