The concentrate of the first developer a tetenal e-6 kit is dark yellow with some deposit. Do not know if it is still good. Since the first dev is a b&w developer, can I change it to anothe b&w developer? If so, which one? Can XTOL or rodinal do the job (the ones I have here)? PS: How can I test the FD to see if it still go? Develop a bw film with it?