"Pete" wrote:

I took an acid reading
This was much easier then my red wine.

I got 2.10*.25 = .525

This doesn't seem good.

Not "good", but not unexpected. Different types of apples range from (and
average of) .20 to 1.3. What kind(s) did you use?

I have some acid blend.
How do I figure how much to add per gallon to raise it.

If your acid blend says 1 tsp per gallon = .15 increase in TA, then
Teaspoons to add = (target TA - measured TA) / .15 x gallons of must.

If your acid blend says 1 tsp per gallon = .12 increase in TA, then
Teaspoons to add = (target TA - measured TA) / .12 x gallons of must.

If it doesn't say either, it is safest to use the first formula, which will
result in a smaller addition.

Assuming you agree with my target of 0.7%:
(0.7 - .525) / .15 = 1.167 x gallons of must
or (0.7 - .525) / .12 = 1.167 x gallons of must

If your acid blend says so many grams per gallon (rather than teaspoons),
use the same formula, but substitute the grams-per-gallon for the
teaspoons-per-gallon figure, and weigh the blend, rather than spoon it.

Or, add acid to a few samples, until you get the taste you prefer, and then
add the same ratio of acid to must as in that sample.