Frog SooTHe™ Total Hardness Increaser for Hot Tubs & Swim Spas 2lbs Swim Spa Fitness Accessory Bottom Center Hole Diameter: 2

Bottom Center Hole Diameter: 2 1/2"

it will most likely work on your hot tub cover

Please Note: FROG makes Serene Bromine cartridges in yellow

The particles are too small to be filtered

Frog SooTHe™ Total Hardness Increaser for Hot Tubs & Swim Spas 2lbs Swim Spa Fitness Accessory Bottom Center Hole Diameter: 2Frog SooTHe Total Hardness Increaser raises the total hardness level (also known as calcium hardness) of your hot tub or swim spa water. Includes the FROG TruDose Cap for precise, no mess measuring. Active Ingredient: 100% Calcium Chloride Dihydrate Size: 2 lbs. Frog SooTHe Total Hardness Increaser is compatible with all spa water sanitization systems including: silver ion granulated chlorine systems, salt systems, granulated bromine, bromine tabs