BioGuard Burn Out Extreme is a single use sachet of chlorine, ideal for shocking swimming pools, treating chlorine demand or dealing to algae problems. It is simple to use. Just cut the top and pour it into your skimmer box. There is no need to measure or pre-dissolve making it easy to use and convenient. Take care not to inhale the fumes when adding to the pool. As it’s name suggests it is extremely powerful.