Just order a Saifert kit for Mg, Alkalinity, Calcium and pH, those are the ones that will really get you where you want to be. Check out Marine Depot or
Premium Aquatics for the test kits, or shop for a pH meter like the PinPoint, about $90 US on the net.
Ordering these kits from one of the e-suppliers can be second day air shipped for less total than you'll pay in LFS stores, and you won't have to deal with bogus info like blindly using buffer from OOD kits. Any decent shop should have considered the conditions of the tank first (like ask enough questions about issues to be in doubt of the results at 7 pH)
HTH