I want some advice regarding a long shelf life liquid paper developer concentrate similar to Rodinal or HC 110 for film. Mixing dry chemicals is not what I want and I also desire deep blacks using FB VC paper such as Ilford MG IV or Adox 110.
Currently I use Ilford MG paper developer but a 5 L plastic container lasts more than 6 months and turns a deep brown towards the end. Is there a way to test to see if this developer (about 9 months old since opened) is still good?
Currently I use Ilford MG paper developer but a 5 L plastic container lasts more than 6 months and turns a deep brown towards the end. Is there a way to test to see if this developer (about 9 months old since opened) is still good?

