Over time, sunlight exposure affects the chlorine in swimming pool water, causing it to work less efficiently. HTH Chlorine Stabilizer helps protect and extend the life of chlorine in your swimming pool so it stays more effective for longer. If you're using an unstabilized chlorinator, adding stabilizer separately can help slow down the effects of direct sunlight on the chlorine levels in your pool. HTH PLUS Chlorine Stabilizer is great for all pool types, including vinyl-lined pools and salt water pools.