Also Known As: Trichloroisocyanuric

An organic compound, trichloroisocyanuric acid or trichlor is an extremely concentrated chlorine, used as a disinfectant, algicide and bactericide in swimming pools and spas.

Because chlorine is naturally unstable, cyanuric acid (CYA) is added to the chlorine. In dichlor, two molecules of CYA are added to one molecule of chlorine. To create trichlor, three molecules of CYA are added. The cyanuric acid extends the life of the chlorine by shielding it from ultraviolet rays.

Unlike dichlor, trichlor dissolves very slowly. It is also very acidic. These traits influence how trichlor should be used in a pool or spa. First, it should never be added to the skimmer, because it can damage equipment. Instead, it can be added to a floating dispenser that allows it to slowly dissolve or via an inline feeder. Trichlor should never be mixed with other chlorines. When added to a chlorinator, the fumes can be strong, so be sure to wear personal protective equipment, including a mask, eye protection and gloves.

Trichlor is generally sold as large tablets, or hockey puck size, which can last up to a week in a chlorinator or floater. To counter the acidity introduced by the trichlor, it may be necessary to add a base to the pool water, so that the pH is balanced.

Using trichlor can lead to a buildup of cyanuric acid. This buildup can make chlorine ineffective, even in normal levels. In this situation, the pool must be drained and refilled or the water shocked with high amounts of chlorine.