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Hey everyone! I'm a new pool owner here in sunny California, and I'm trying to get my water chemistry balanced. I've been testing my pH with the phenol red drops, but when my free chlorine (FC) is above 10ppm, the test turns purple instead of the usual red/orange/yellow range. It's throwing off my readings! Can anyone explain the science behind why high chlorine messes with the pH test? I'm all about understanding the 'why' behind things—helps me stay centered and mindful, even with pool maintenance! 🧘‍♀️

Oh man, I feel you on this one! As a sleep-deprived parent, I barely have time to test my pool, let than figure out weird color changes. But I've been through this exact thing last summer. From what I remember (and please, someone correct me if I'm wrong—my brain is mush from toddler wake-ups), high chlorine levels can actually *bleach* the phenol red indicator. It's like when you leave a colored shirt in the sun too long and it fades, but here it's messing with the dye in the test reagent. So when FC is above 10ppm, the test can't show the true pH color because the chlorine is interfering chemically. I think it gives a false high pH reading (that purple color) because the indicator gets oxidized. Hope that helps... now back to my coffee. ☕

Thanks, FloatFreak42! That bleaching analogy really helps visualize it. So it's not that the pH is actually super high—it's that the test itself is compromised. I did some digging, and you're spot on: phenol red is a pH indicator dye that changes color based on hydrogen ion concentration (acidity/alkalinity). But when there's too much chlorine (an oxidizing agent), it reacts with the dye molecules and alters their structure, shifting the color toward purple/violet. That's why the test reads falsely high. For accurate pH, you need to either dilute the sample with distilled water to lower the chlorine concentration first or use a different test method when FC is high. Science is so cool—it's like chemistry yoga for the pool! 🌊✨

Exactly! And as a practical tip from one tired pool owner to another: if you're shocking your pool or have high FC, just wait until the chlorine drops below 10ppm before testing pH with phenol red. Or yeah, dilute it—I've done that in a pinch. Honestly, I mostly just try to keep my FC in the 3-5ppm range to avoid this headache altogether. Less science, more sanity for me. But glad you're getting into the details, CurrentCaptain36—maybe you can teach my kids about pool chemistry someday so I can nap. 😴 Keep those vibes balanced!