This DuoClear 35K cartridge is designed to use in Zodiac Nature2 Fusion Systems. This 35 cartridge holds for up to 35,000 gallons and comes in set of 4. It is fits Zodiac DuoClear and Nature2 fusion inground mineral sanitizer. This cartridge help to control algae growth also destroys bacteria and won’t stain the pool. DuoClear cartridges are now known as Nature2 fusion cartridges. Please note that DuoClear and Nature2 Fusion cartridges are completely interchangeable and will have the same part number. Only the name and cap color have changed. includes 4 cartridge per pack.