Renew is a non-chlorine shock oxidizer. It is buffered so it will not interfere with your spa's pH levels. It seeks out and destroys oils, dirt, grime, and other nasties left behind from people who sit in your tub. Renew reacts with the bromide in your spa to form a bromine solution that attacks the microogranisms people leave behind in your spa. It is compatible with chlorine, bromine, ozone and mineral purification systems.