If your tank is only 2 weeks old, I wouldn't worry about the pH yet. some acids produced in the cycling process can naturally drive down the pH in a SW
tank. Wait until the tank has fully cycled, then tackle one issue at a time. Also - I wouldn't be adding magnesium, unless you have a test kit which verifies low levels. Again, not something to worry about until the tank has fully cycled, and other parameters have stabilized.
My substrate is crushed coral and of course that should be helping matters.
Not really. CC
and Aragonite sand do not have the buffering capabilites once suspected. What CC
really does is maintain elevated nitrate levels. At this point, where the tank is fairly new, I would strongly consider removing any CC
Fish-only or reef tank? For a reef, you should be at about 1.025 at 80F.
Don't stress about the numbers yet. The only thing you should be really testing for right now is A/N/N. Yes, keep an eye on the pH - so you have a baseline to work with once you've finished cycling. Tans that are kept in houses where all the windows are closed also have typically lower pH, as do covered tanks, and tanks where water flow/circulation in less than optimal.
Take a deep breath...and good luck!