I used to use DDX some years ago. From the one liter bottle, I filled 4 small brown glass bottles. I kept my developer between 6 months and one year. But while the developer is still usable, the grain grows and the image appears reticulated. As the developer is quite expensive, I do not recommend the use beyond 6 months. I stop to use it and switch to LC29 which is more versatile and retains its qualities much longer. From my experience, DDX as the same micro contrast and tonal distribution than ID-11 1+1 with a 2/3 stop speed loss (with ID-11).