SpaGuard Spa Sentry (1 qt) SpaGuard Spa Sentry pH Balance for Spas and Hot Tubs SpaGuard's Spa Sentry gives spa owners a one-step liquid additive to avoid pH bounce for up to 1 month per application, simply by adding directly to water. Before using this product 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 1 Quart Bottle