The PETA Zinc Dispenser is designed to use either heptahydrate or monohydrate (Mono Zinc). If using zinc sulphate heptahydrate no dissolving is needed. Just put the crystalline salt directly into the container.
If using Mono Zinc (zinc sulphate monohydrate) always pre-dissolve it in water before putting in the Zinc Dispenser. One litre of water will dissolve up to 550 grams Mono Zinc (if immediately stirred after being added).