SpaGuard Stain & Scale Control (1 qt) (3 Pack) SpaGuard Stain & Scale is a liquid sequestering agent. Scale or calcium carbonate build-up can cause damage to your spa surface as well as your circulation system. SpaGuard Stain & Scale Control does a great job of preventing scale by introducing powerful agents that bond to problem-causing calcium ions in your spa water. Product Information: pH 3.0 Prevents scale formation and cloudy water due to high calcium levels Removes some scale buildup on spa surface Removes relatively fresh metal stains from spa surfaces Directions for use: 1. Clean filter 2. Apply 1 ounce per 300 gallons directly to the spa or hot tub 3. Let pump run at least 2 hours after treatment 4. Add 1 ounce per 300 gallons weekly for maintenance