I find gypsum requires a ridiculous amount of stirring to dissolve at room temperature. But added cold, by the time the liquor has reached strike temperature, it has taken care of itself with no effort needed.
If it is not dissolving, here's a tip I remember Martin has provided: gypsum can convert to or be contaminated with chalk (calcium carbonate,) which of course is insoluble and useless for brewing. Put a drop of acid on your gypsum. If it bubbles, some of it is chalk. Replace. Hiding it in the grist will only be sticking your head in the sand.
(I think the same test applies to pickling lime, or maybe I'm remembering this all wrong. Martin will surely correct me.)
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