INLINE DI RESIN CARTRIDGE: Direct replacement for the Aquatic Life RO Buddie +DI system; This mixed-bed deionization filter reduces Total Dissolved Solids (TDS) to zero, giving you the purest water for aquariums COLOR-CHANGING RESIN: Resin changes color from blue to tan when exhausted, so you’ll always know exactly when it’s time to replace ULTRA-PURE WATER FOR AQUARIUMS: Removes the final dissolved minerals and debris after RO filtration, producing water that’s extra clean and gentle for sensitive fish and plants EASY INLINE DESIGN, REFILLABLE HOUSING: Connects with standard ¼” tubing using press fittings at each end. Installs quickly into your RO Buddie +DI system without tools; he translucent cartridge comes with a removable cap so you can refill it with Aquatic Life bulk DI resin SUBSCRIBE AND SAVE FOR CONVENIENCE: Never run out of filters—enroll in the Subscribe and Save program for automatic deliveries at your chosen frequency and enjoy extra savings with each order