How should S-26 Gold 4 be stored, and how do I know the pack is genuine?

Keep the pack tightly closed in a cool, dry place away from heat, humidity and strong odours, use a clean dry scoop, and finish the powder within the after-opening period stated on the pack. Buy only from authorised, reputable retailers and check that the seal, product name, age indication, batch code, expiry date, importer details and local-language labelling are all present.