I am curious - what is the effect on your negatives when developer starts to go bad? For example, I keep Xtol in a tank with a floating lid and a stopcock at the bottom. I draw it down to dilute 1:3 and throw out it out after processing. I use an expert drum and do not do a lot of sheets, so it may take me 3 or 4 months to go through a batch. I still get crisp, full range negatives at the end - assuming the exposure is correct - but is there something else that I might be losing?