The first time I used Xtol (1 ltr pack) I had problems mixing it at room temperature. Since then I have always mixed it at about 35 degC & have had NO problems ( touch wood). I now use the 5 ltr packages & store it in collapsable containers to keep out the air. This way the developer seems to keep forever. Using Xtol @ 1:1 it lasts me about 6 months with no visible change in results. With the negative feedback on Xtol & the discontinuation of some B&W products I fear Xtol may soon bite the dust. Some of us however are quite happy with the product.(posted 8272 days ago)