I keep my XTOL stock solution no more than 2 months. I mix with filtered water and have never had the dreaded XTOL failure. However, the XTOL dies very abruptly after 2 months in one of those accordion type containers. I'm using the glass bottle & marbles system now & I'm hoping that I can coax an additional month out of the stuff. I have used tmx & tmy in Xtol with good results. The best results are with 400 Delta in XTOL. 1:1 dilution btw.(posted 8650 days ago)