I would add 1.9 gallons (7.2 L) of water without acid to get your brix and TA adjusted.
So these are the numbers that I used to make this estimate.
12 gal x3.785L/gal= 45.4 L juice
Added 4tsp (~20g ) tartaric acid so 20g/45.4L =0.44 g/L so TA is now ~0.84 g/L
I like to use brix to calc sugar dilutions. 1.108 =25.5 brix to dilute to 22 brix need to add 7.2 L of water. If you just add water, then your TA would drop to 0.73.
So these are the numbers that I used to make this estimate.
12 gal x3.785L/gal= 45.4 L juice
Added 4tsp (~20g ) tartaric acid so 20g/45.4L =0.44 g/L so TA is now ~0.84 g/L
I like to use brix to calc sugar dilutions. 1.108 =25.5 brix to dilute to 22 brix need to add 7.2 L of water. If you just add water, then your TA would drop to 0.73.