Free Chlorine vs. Total Chlorine: What Your Test Strip Actually Means
Your test strip shows two chlorine readings: Free Chlorine (FC) and Total Chlorine (TC). Most pool owners focus on free chlorine and ignore total chlorine, but the relationship between the two tells you something important about your water quality.
Free Chlorine: The One That Works
Free chlorine is the active, available chlorine in your pool. It's the chlorine that's ready to kill bacteria, destroy algae, and break down contaminants. When someone says "your chlorine is at 3 ppm," they're talking about free chlorine. The ideal range for free chlorine is 1-4 ppm, with 2-3 ppm being the sweet spot for most pools.
Total Chlorine: The Bigger Number
Total chlorine is the sum of all chlorine in your water, both free (active) and combined (used-up). Total chlorine is always equal to or higher than free chlorine. It can never be lower.
Combined Chlorine: The Hidden Problem
Combined chlorine (also called chloramines) is the difference between total chlorine and free chlorine. You won't see it as a separate reading on most test strips. You calculate it: TC minus FC equals combined chlorine.
Combined chlorine forms when free chlorine reacts with nitrogen-based contaminants like sweat, urine, body oils, and sunscreen. It's the compound responsible for that strong "chlorine smell" at indoor pools and red, irritated eyes. Ironically, a pool that smells like chlorine usually doesn't have enough free chlorine.
When to Worry
If your total chlorine and free chlorine are equal (or very close), you're good. That means almost all your chlorine is working.
If your total chlorine is more than 0.5 ppm higher than your free chlorine, you have a combined chlorine problem. For example: TC of 4 and FC of 2 means combined chlorine is 2 ppm. That's significant.
The fix is breakpoint chlorination, commonly known as shocking. You need to raise your free chlorine to 10x your combined chlorine level. This overwhelms the chloramines and breaks them apart. For a combined chlorine of 2 ppm, you'd need to raise FC to about 20 ppm, which is a heavy shock.
What Pool Clarity Does
When you enter both free and total chlorine readings, Pool Clarity calculates your combined chlorine automatically and tells you whether you need to shock. If you do, it calculates the exact amount of liquid chlorine based on your pool volume and current levels.
Let Pool Clarity do the math.
Enter your test results. Get exact dosing instructions for your pool.
Try Pool Clarity Free