What Combined Chlorine Actually Tells You
It is the test result most pool owners never look at, and it is the earliest warning a pool gives. Combined chlorine explains the strong "chlorine" smell, the red eyes, and water that tests fine but does not feel right. In this video, Next Wave Pool Care explains what combined chlorine is, how to find your number with one subtraction, and the breakpoint fix that burns it off.
Here is a test result most pool owners never look at, combined chlorine. Your total chlorine is free chlorine plus combined chlorine. Free chlorine is the chlorine ready to work. Combined chlorine is chlorine that already fought something and lost its strength. When combined chlorine climbs, the algae and bacteria are winning, even if the water still looks clear. That number is your early warning. If your pool smells strongly of chlorine, that is usually combined chlorine, too. The fix is more free chlorine, held high until the combined number drops back down.
## Where Combined Chlorine Comes From
So, where does it come from? Combined chlorine is really chloramine, free chlorine that already grabbed onto sweat, body oils, sunscreen, and swimmer waste. It still shows up on your test, but it barely sanitizes anything. Here's how you find yours. Test total chlorine, then subtract the free chlorine. That difference is your combined chlorine. If it reaches 0.5 parts per million or higher, your water needs help, even when it still looks clear.
The fix is called breakpoint chlorination. You raise the free chlorine to about 10 times the combined number and hold it there until the chloramines burn completely off. Then, test again. And that strong pool smell? That is chloramine, not too much chlorine.
## Key Takeaways
- Total chlorine is free chlorine plus combined chlorine; combined chlorine is chlorine that already fought something and lost its strength, so it barely sanitizes.
- Rising combined chlorine is an early warning that algae and bacteria are winning, even while the water still looks clear, and the strong "chlorine" smell is usually chloramine, not too much chlorine.
- Find your number by testing total chlorine and subtracting free chlorine; at 0.5 parts per million or higher, the water needs help.
- The fix is breakpoint chlorination: raise free chlorine to about 10 times the combined number and hold it there until the chloramines burn off, then test again.
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