I read somewhere that the Vitamin C derivative in Xtol is the main developing agent even though it contains phenidone (or derivative) as well. Since Vitamin C is good for us, maybe it's good nutrition for some biological life that might be breeding in the solution, maybe mould or something. If it were being eaten up, development would be reduced.(posted 8419 days ago)I've never lost a negative through a chemical or film problem. The thought of losing a roll due to Xtol failure is unacceptable. My time and opportunities are too valuable. So I don't use it even though I'd like to.