This is another alternative to chlorine, known as Potassium Monopersulfate or MPS.
When chlorine is used to oxidise pool water it forms chloramines which produces an odour, but because active oxygen doesn’t contain chlorine, when it is used to oxidise pool water it won’t leave any smell.
It’s not as sensitive to sunlight as chlorine and bathers can re-enter the pool a short time after the water has been shock treated with active oxygen unlike chlorine.
It also works well as a shock treatment alongside a weekly chlorine treatment. While active oxygen is a strong oxidant, it is not a sanitizer, and therefore provides no protection against bacteria and viruses. It is also more expensive than chlorine.