I had one failure only because I didn't know roughly when stock solution A would expire. After a few months it died. Since it has a rather short shelf life, I mix up only 100ml of stock A. Stock B lasts indefinately so I mix up 1000 ml. I remember that as stock A ages, it also changes colour slightly...that was when I discarded and mixed a new batch. I haven't mixed any up for a while (about a year ago) so I don't rememeber the colour of freshly mixed and slightly aged. I'm sure Sandy will read this and chime in!