I have mixed 5l xtol in 2,5l of water about 10 months ago. I haven't used it in last 6 months, when it was ok. Now I need it. The roll is waiting and I really do not want to risk it. From what I searched in older posts concentrated xtol is probably all right if kept in right conditions. Hovever, im not quite sure if its so in my case. I have two bottles of it. One about half full, PVC (black tetenal bottle), filled with lighter gas, and other is full, hama photo bottle. But its HDPE bottle which, as I've read recently is bad for storing developer. I'm also not entirely sure if the xtol in the PVC bottle is concetrated. But its unlikely its just stock. It seems that I have to do some testing. I read about xtol sudden death, but its rather anecdotal and I do not know if assumption that it either works or not is right. Is it? I would make testing very simple. Unfortunately I do not have any unexposed films I used to develop in xtol in the past. I think I could make test it against rodinal or id11 (thats what i have) and see if it produces similar density when it should. However I'm not sure if manufacturers dev times are to be trusted as I have rather mixed experience, particularly with ilford data. It would be most convenient to test it with tmax400 expired in 95.