HTH® ultimate Shock treatment delivers an incredible value with a 7-in-1 formula that increases chlorine levels, kills and prevents bacteria and algae, reduces eye and skin irritation, prevents stains from metals and prevents scale. HTH® makes pool care easy with a shock treatment that you can apply directly to the pool and see crystal clear results in just 24 hr. This pool shock is ideal for all pool surfaces and won't fade your vinyl pool liner. You can also use this swimming pool shock in your salt water pool for the same sparkling clear results.