You'll want to understand the relationship between calcium levels and carbonate hardness.
Knowing your calcium level is only part of the equation. You also want to know your carbonate hardness and keep it around 8 to 11 dkh.
Adding the purple should increase your calcium levels, but if your carbonate hardness is too low it's not going to give you the results you want. You really want a two-stage process that includes a buffer to keep carbonate hardness at target levels.
Not sure when you're planning to add corals, but if it's a ways off, there's really no pressing need to get calcium levels up now. You'll just probably deplete those levels when you do water changes.
Get a good two-stage buffer and calcium product and test kits. Shortly before adding corals it's a simple matter to get to your targets (say, 9.5 dkh and 420). If something is screwy, check magnesium which is a 3d variable that's important.