Why do the chlorine levels in the pool seem so hard to maintain on bright, sunny days?
Well, for one thing you probably have more bathers (and therefore more bather waste) on a sunny day than on a cloudy day and it will often be warmer on a sunny day. These factors tend to increase the chlorine demand. But even without the extra bathers or higher temperatures bright sunlight itself can have a devastating impact on chlorine. Depending on other factors such as water depth, temperature, etc. bright sunlight can destroy 3/4 of the chlorine in pool water in an hour or so. By adding 25 PPM of cyanuric acid (“stabilizer” or “conditioner”) to the pool water, the rate of chlorine loss can be cut by two-thirds.
