So can we conclude then that if you have the choice, reusing a PET bottle to store mixed developer in is a better option than reusing a HPDE bottle? For stop and fix, I don't think it matters. And if the PET bottle gets brittle after a few years, you just replace it with another PET bottle that was otherwise going into the recycling. My Se toner bottle is at that point and I just finished a bottle of Tonic. Lucky me.