The best way to add calcium

[Delphinus]

Uh, no. I don't know what all brands say on this, but I used to use Seachem 2-parts (Reef Builder for alk and Reef Calcium), and the instructions said to wait at least a half hour between the two. I myself found it simpler to get in the habit of adding one in the morning and one at night, but YMMV of course.

Since the Seachem stuff is powder I would predissolve the stuff, and I found if I had just the slightest amount of residue on my stir stick from the previous mix, the reaction was so exothermic that the water would literally be boiling hot for an instant (if I had my hand under just the right spot). Then there would be an instant coating of calcium carbonate where the two additives had mixed.