The new version of the DURATION tabs are junk. They are 48% cal-hypo and they don't last days without dissolving, they barely last hours. The older ones were wrapped in a plastic capsule that worked far better. HTH's sister company, PoolLife (another Arch Chem company) still sells them as PoolLife Active Cleaning Caplets. But their website doesn't say the active percent of Chlorine...typical of Arch.