Tank Chemistry

So I started to add some LPS and one small SPS to my tank to give it a shot. Trying new things with baby steps to learn how this hobby works.

So its been awhile since I measured Cac, Alk and Mag. I did it for a couple weeks with no changes. LFS said I should be good with the LPS and SPS because they are small and I will replace most of the missing elements in water changes each week.

Yesterday I wanted to measure the element after 2 days from a 10% water change (75 gallon tank, 20 gallon slump).

320 - 350 Calc
9.7 - 10.2 Alk
1470 - 1510 Mag

Hard to be sure of the measurement number looking at the syringes. So I see that my calc is low. What would be the next course of action for my tank?

Wait a day then measure again to see the loss rate of the elements?
Purchase 2 part to bring up Calc?
Purchase Kalkwasser and does with auto top off?

Thanks for the help again. Just want to make sure I take the correct next step.