SpaGuard’s Spa Sentry gives spa owners a one-step liquid additive to avoid pH bounce for up to 1 month per application, by merely adding directly to water. Before using SpaGuard Spa Sentry, you must first drain and refill your spa and set the desired level of both pH and alkalinity before applying. Spa Sentry also contains a clarifying agent that removes dissolved metals in your water, giving your spa clearer and softer water that will be instantly noticed by bathers.