The HOTSPRING HOTUB Spa Mineral Ion Cartridge 3-Pack Sticks are designed specifically for use in hot tubs. Made by the brand Hotspring Hotub, these cartridge filters are easy to install and provide a 4-month supply of mineral ions to help maintain clean and clear spa water. With a capacity of 800 gallons each, this set includes 3 cartridges, making it ideal for continued use in your hot tub. Made in China, these cartridges are a convenient and effective solution for keeping your spa water healthy and refreshing.