Instant ocean salt parameter

[Aquattro]

IO is lower in Ca, higher in alk. I would dose Ca in your new water and then maintain it with your chosen method between water changes. The alk numbers are fine, IMO.
Mg, I usually don't care about. I add some now to my new water, but see no difference vs when I didn't do anything with it. I'm still not sold on the whole Mg thing..