I'd just follow the regeneration instructions from Seachem, as follows,
Regeneration: Soak in a 1:1 bleach:water solution for 24 hours in a non-metalic container in a well ventilated area and away from children.
Rinse well, then soak for 8 hours with a solution containing 2 tablespoons of ChlorGuard™, Prime®, or equivalent dechlorinator per cup of water.
Original color and full activity should now be restored and Purigen® is ready for reuse.
Eheim Pimpette #270
Eheim Pro II 2028; Classics Series -2215, 2217, 2260, 2262; Pro 2229 Wet/Dry