Pool Water Chemistry Logger

Field guide: Pool Water Chemistry Logger

Pool chemistry is a two-variable game pretending to be complicated: free chlorine kills what swimmers bring in, and pH decides whether that chlorine works — at pH 8.2, over 80% of your chlorine is in the lazy hypochlorite form versus the potent hypochlorous acid that dominates at 7.2. This logger holds both in the MAHC operating bands (FC ≥1 ppm, pH 7.2–7.8), plus the supporting cast: total alkalinity (the pH stabilizer), cyanuric acid (sunscreen for chlorine that smothers it past ~90 ppm), and spa temperature against the 40°C safety max.

For public pools the log IS the compliance artifact — health codes require chemistry records at opening and through operating hours, and the printable report here matches what inspectors ask to see. For everyone, the trends tell the maintenance story: chlorine demand climbing week-over-week means a building organic load (time to shock), pH drifting up relentlessly is the plaster/aeration signature, and CYA only ever ratchets upward until you dilute.

Field tips

• Test pH and chlorine BEFORE adjusting anything, and log first — sequence discipline is what makes trends diagnostic.
• If chlorine reads fine but the pool smells 'like chlorine', that's combined chloramines — the fix is more chlorine (shock), not less.
• CYA never goes down by chemistry, only dilution — when stabilized tabs push it past ~50–90, plan a partial drain, not more product.

Records are stored only in this browser (localStorage) — export regularly. This tool aids field documentation; it does not replace your agency's official inspection procedures or engineering judgment.