Thanks for the advice. I did use distilled water but stirring was always vigorous, I tried to prevent too long exposure in the mixing vessel. I used ground glass stoppers but I think I will switch to plastic capped ones. The use of bisulfite was intended to keep the solution from being acid, but maybe this is futile as ppd is alkaline itself.(posted 8413 days ago)But I would appreciate if Patric would advise whether the solution turns dark in color at all since February?
Thanks once again!