Dont you mean, the tan you are using is sold from Orion Taxidermy Supply? Anyway, the tan isnt in question here.
Sounds to me, like you are adding acid to the same pickle, over and over again, while ATTEMPTING TO MEASURE SALT CONTENT. That is virtutally impossible without some type of professional water testing.
Salinometers are rendered USELESS after a pickle is used ONE time. The density of the water changes from, we'll just say, "skin trash". About the only thing you can do, is "guestimate", and add 1/4 lb per deer cape, that you remove from the pickle, before adding new ones. Skin sizes would dictate that "guestimation".
One very good reason no to re-use a pickle more than once. Shouldnt re-use at ALL!
To make a long story short, NO, you did NOT tan those capes, if they were still acidic. That type of tan, will only fix to collegen with a pH of 4.5 and HIGHER.
For formic acid: Every gallon of 80degF water, 1/4lb salt, 2oz baking soda, for SEPERATE NEUTRALISATION BATH, for 45-60 minutes.