Seachem. Purigen
Directions at the bottom:
Rinse before use. Use in a fine mesh filter bag. Each 1 L treats up to 4,000 L (1,000 gallons*) for up to six months. Exhaustion is indicated by a pronounced discoloration of the beads to dark brown or black.
Regeneration: Soak in a 1:1 bleach:water solution for 24 hours in a non-metallic container in a well ventilated area and away from children. Use regular 8.25% hypochlorite household bleach (non-scented, no dyes, do not use a splash-less bleach). Rinse well, then soak for 8 hours with a solution containing 4 tablespoons of Prime®, or equivalent dechlorinator per cup of water. Rinse well. For freshwater use, soak for 4 hours with a solution containing 2 tablespoon of buffer per cup of water (Discus Buffer®, Neutral Regulator®). Original color and full activity should now be restored and Purigen® is ready for reuse. Caution: some slime coat products may permanently foul Purigen® and render regeneration difficult. Do not reuse if odor of bleach/chlorine is detectable. In case of doubt, soak beads in small quantity of water and test for residual chlorine with a chlorine test kit.