I'm thinking of trying D316. I have two questions.

1. If I use a bit more propylene glycol, say to make 25mL of concentrate instead of 20mL, will that make it easier to dissolve and less likely to crystallize, or will the different concentration of metaborate alter the solubility of the ascorbic acid? I would obviously use 25mL of the concentrate to make 1_L of working solution.

2. Whichever version of sodium metaborate I have, it shouldn't make any difference, should it? In my post above where I pasted Ryuji's comments about the naming of sodium metaborate (tetrahydrate and octohydrate) although the theoretical compositions of the two compounds give very different molecular weights (one double the other) it seems to me that 2.2 grams of either is exactly the same when dissolved. I have bought chemicals from a supplier who has been generally a bit slack with noting water of crystallization, which usually makes a difference but not, I think, in this case. It's been a while since I did high school chemistry (1965).