My mead is aging away in secondary, about 2.5 months old right now. I just checked it and the SG is 0.992 and the PH is lower than I can measure. It tastes really tart. The SG is fine and where I'd expect given I used premier cuvee, but the acidity worries me. Can I fix this? Should I add calcium carbonate? How much? 5 gallon batch BTW.