Form of chlorine that uses cyanuric acid as a base. Usually in tablet or stick form, but occasionally comes in granular. Used for daily chlorination. Tablets and sticks are designed to break down according to the temperature of the water (warm water - very fast, cold water - very slow) have a long shelf life, very convenient usage (tablets or sticks can last up to a week in water temperatures up to 93 degrees f., and are very precise in adjusting residual chlorine), usually are 97 -99% sodium trichloro, 1 - 3% inert, active chlorine measurements are disputed amongst the manufacturers so don't be misled by inaccurate labels. It was designed to last for long periods, without replenishing, should not be considered as use as a shock, as it can take DAYS for the chlorine to drop back down to a swimmable level!