I think I read that the way to bring the acid back into balance is to add an alkali salt like Calcium Carbonate. The problem with that is if you add a lot, it tastes chalky..... get a glass with a known volume and add a known amount of CaC03 and see where you get would be my suggestion. If the glass is 4 oz and there is 1 gallon of wine, that would be 1 part in 32, so if you addeded 1/8 tsp of CaC03, you'd need 1/8*32=4tsp of Calcium Carbonate.
But again. I'd heard that this can be a problem as it can add a chalky flavor. There maybe be other bases to use, I can't think of them off the top of my head.
