Perhaps my best bet would be to start over with an MQ-borax solution in water, like the basis of d-76 without sulfite. With enough borax, the buffering ought to be strong enough to minimize pH changes from no additive to either sodium sulfite or sodium ascorbate. In either case, I would be using the same molar concentration as was used in the experiments I referred to before. However, if there is a change in pH, it should favor the sulfite as sodium ascorbate solution itself is not likely to be higher than 7.6 according to Merck.

I do not have a way to check pH. I will search the local swimming pool supply places for pH indicators that might narrow it down, at least for differential readings. I am 50 miles from the nearest moderate sized cities and 100 miles from the next size up. Otherwise it's internet or mail, and I'm too impatient.