Obtaining a 27% saturated solution of potassium sulfite

Hello,
I decided to continue my experiments with H&V Control. To do this, I want to make a solution B that contains 14.28 g of potassium carbonate and 26.91 g of potassium sulfite. Since there is no way to buy potassium sulfite, I want to use a replacement with 18.89 g potassium bicarbonate + 9.55 g KOH in 100 ml water. In the "Resources" section for making potassium sulfite concentrate say that saturation of up to 65% of solution can be obtained. Sounds good, but the solubility of potassium metabisulfite is only 22.4 g/100 mL. What is the procedure for obtaining sulfite?

Not sure about your figure for the solubility of potassium metabisulfite, this source has it as 49.5g/100ml at 25C:


From the molecular weights I get that 43g metabisulfite provides 65 g sulfite so the resources section appears correct on that.

Well... who knows what I watched

Ok, that answers my question, but there's only one thing left - how do I know how far I've gone with the soup. Maybe my potassium metabisulfite is good, but KOH never gives it in good purity - usually in the 85% to - range. Even from reputable manufacturers like Merck. I'm worried that the pH could be seriously off, and I can't find any information anywhere about what the pH of the H&W Control developer should be...

It looks like I will have to make a solution according to the classic recipe and measure it. I expect that to this developer in particular, pH matters a great deal.