I have 4 carboys of unpasteurized grape juice that started fermentation in mid to end of September. No yeast was used. I've been making wine for a few years without any testing equipment but just last week I acquired a pH tester and used it today to test my wine. The reading show a pH of 3.9 for muscat, 3.92 for burgandy, 4.07 for merlot and 3.95 for cabernet sauv. I've read that tartaric acid can reduce the pH but should be added prior to fermentation. Can I add it now since fermentation is completed? The recommended amount to add was listed at 1 g/L of wine to reduce the pH by 0.1 unit before the start of fermentation and 2 g/L if the wine is cold stabilized? What are your thoughts and recommendations as to what I should do?