Do you have a calibration solution for the refractometer and do you calibrate frequently? As someone who has been around marine systems for decades, and having been caught fixing symptoms and not the root cause, making sure you are starting with the simple things is important. I had a number of issues a few years ago, I couldn't figure out what was going on. Turns out my calibration solution was leaking and I was trying to figure out why my salinity was constantly changing.I’m using reef crystals for salt, api for test kits and a refractometer
RC mixes up way way high in Alk, Ca and Mg. I am surprised you are all the way down to 7dKH and 360ppm Ca. Hence the salinity questions.
If you are certain salinity measurement is correct, then I would still do some more water changes instead of raising the levels with Ca mixture and NaCO3. The reason is that if your other levels are so far from where they should be with that salinity, then Mg, and everything else is bound to be off a bit as well. And water changes generally don't hurt anything, unless you are bringing Nitrogen and Phosphorous too low, or salinity and temperature aren't proper.
If you don't feel like any more water changes, adding Ca and CO3 is the next best thing for sure.