The cheat sheet didn't start with chlorine. It started with a word: Comfort . pH 7.4–7.6: The eye of the needle. Above 7.8, chlorine sleeps. Below 7.2, it eats your skin, your liner, your patience. Mark had poured in shock—bags of the stuff. But his pH was off the charts (8.2, he later learned). The chlorine was present but useless, like a guard dog locked in a soundproof room. The cheat sheet explained: Total Alkalinity is the mattress; pH is the sleeper. Adjust the mattress first (80–120 ppm), then tuck in the pH. He added sodium bisulfate (pH down) and felt the water sigh.
And then, a note on calcium: Calcium Hardness (200–400 ppm): Too low, and the water eats your plaster like a sugar cube. Too high, and it rains scale—white flakes of regret on your tile line. pool chemical cheat sheet
The middle of the sheet was a cautionary tale. Cyanuric Acid (CYA): Sunscreen for chlorine. 30–50 ppm. Above 100 ppm? You've built a prison. Chlorine can't escape, but it can't work either. Only draining the pool sets it free. Mark tested his CYA. 180 ppm. He had been using stabilized chlorine tablets for three years. Each tablet added a little chlorine and a lot of CYA. He was slowly poisoning his pool's immunity. The sheet’s solution was brutal: Partial drain. No shortcuts. The cheat sheet didn't start with chlorine