Calcium Hardness Calculator

Pool Calcium Hardness Calculator

77% Strength (Flakes) 100% Strength (Anhydrous/Pellets)

Required Amount:

function calculateHardness() { var poolVolume = parseFloat(document.getElementById("poolVolume").value); var currentCH = parseFloat(document.getElementById("currentHardness").value); var targetCH = parseFloat(document.getElementById("targetHardness").value); var purity = parseFloat(document.getElementById("chemicalPurity").value); var resultDiv = document.getElementById("hardnessResult"); var amountText = document.getElementById("amountText"); var adviceText = document.getElementById("adviceText"); if (isNaN(poolVolume) || isNaN(currentCH) || isNaN(targetCH)) { alert("Please enter valid numbers for all fields."); return; } if (targetCH <= currentCH) { resultDiv.style.display = "block"; resultDiv.style.backgroundColor = "#fff4e5"; amountText.innerHTML = "0 lbs"; adviceText.innerHTML = "Your current hardness is already at or above the target. No chemical addition is needed."; return; } var difference = targetCH – currentCH; var amountLbs; if (purity === 77) { // To raise 10,000 gallons by 10ppm, you need approx 1.25 lbs of 77% calcium chloride // Formula: (Difference / 10) * (Volume / 10000) * 1.25 amountLbs = (difference / 10) * (poolVolume / 10000) * 1.25; } else { // To raise 10,000 gallons by 10ppm, you need approx 0.9 lbs of 100% calcium chloride // Formula: (Difference / 10) * (Volume / 10000) * 0.9 amountLbs = (difference / 10) * (poolVolume / 10000) * 0.9; } resultDiv.style.display = "block"; resultDiv.style.backgroundColor = "#e7f3ff"; amountText.innerHTML = amountLbs.toFixed(2) + " lbs"; adviceText.innerHTML = "Pre-dissolve the calcium chloride in a bucket of water before adding it to the pool deep end while the pump is running."; }

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Understanding Calcium Hardness in Pool Water

Calcium hardness measures the amount of dissolved calcium in your swimming pool or spa water. Maintaining the correct balance is critical for the longevity of your pool's surface and plumbing equipment. Unlike pH or chlorine levels, calcium hardness doesn't change rapidly, but it should be tested monthly.

Ideal Calcium Hardness Ranges

The target range for calcium hardness depends largely on the type of pool surface you have:

• Concrete/Plaster/Gunite Pools: 200 – 400 ppm (parts per million).
• Vinyl Liner or Fiberglass Pools: 175 – 225 ppm.

What Happens When Hardness is Low?

When pool water has low calcium hardness (below 150 ppm), the water becomes "hungry" or aggressive. It will attempt to saturate itself by leaching calcium from the pool's surroundings. This leads to:

• Etching and pitting of plaster, grout, and concrete surfaces.
• Corrosion of metal components (ladders, heat exchangers, and lights).
• Shortened lifespan of the pool interior.

What Happens When Hardness is High?

Conversely, high calcium hardness (above 400 ppm) causes the water to become over-saturated. This often results in:

• Cloudy or "milky" water.
• Scale formation on pool walls and floor (rough white patches).
• Calcification of the filter media and heater elements, reducing efficiency.

How to Use This Calculator

To calculate exactly how much calcium chloride you need to add, follow these steps:

1. Test Your Water: Use a high-quality drop test kit to determine your current ppm.
2. Determine Volume: Enter your total pool capacity in gallons.
3. Select Target: Aim for 250 ppm as a safe baseline for most pools.
4. Check Chemical Purity: Calcium chloride is typically sold as 77% flakes or 90-100% anhydrous pellets. Check your bucket label to ensure accuracy.

Practical Example

If you have a 20,000-gallon plaster pool with a current reading of 150 ppm and you want to reach 250 ppm using 77% strength flakes:

• Step 1: Difference is 100 ppm (250 – 150).
• Step 2: In a 20,000-gallon pool, you need 2.5 lbs of 77% flakes to raise it by 10 ppm.
• Step 3: 2.5 lbs × 10 (to reach 100 ppm) = 25 lbs of Calcium Chloride.

Pro Tip: Never add more than 10 lbs of calcium chloride per 10,000 gallons at one time. If your pool requires a large dose, break it into smaller applications spaced 6 hours apart to ensure proper mixing and prevent cloudy water.