Triple-digit summer UV
The Valley runs 100 days a year above 100°F. UV strips free chlorine in hours unless cyanuric acid (stabilizer) is in range — but stabilizer creeps up over time and locks chlorine from working. Your test strip reads fine; nothing is sanitizing. We track the free-chlorine-to-CYA ratio and flag partial drains when stabilizer climbs past about 50 ppm.