Actually, it can be. Liquid chlorine can break down when exposed to light and heat, especially light. But usually high concentration bleach or LC is more vulnerable than low concentration bleach. Just not likely. Still, I've gotten 12% LC that didn't even test at ten, from the now-defunct Branch Brook Pools, and 12% that tests at 14.5 from Sun Pools. The latter consistently tests high...VERY high turnover of their stock.