This is one of my two beloved film developer (the other one is the Bellini’s Hydrofen).
Yesterday I had a new experience with it, and it’s worth to be told. I developed a Fomapan 100 using a 1+50 solution from a bottle opened more or less 6 months ago.
The result was a totally blank film without anything (neither brand or frame numbers). So the developer was totally dead and, when I emptied the bottle, I found that in it there was an hard, brown crust, as if the active part of the developer became a precipitare leaving only a useless brown liquid.
Searching on the net I found another case like mine: it’s here.
So, lesson learnt: when you open a R09 bottle, after 4 months throw it away. And, in case of doubts, try to develop a small film leader to check if it is still working or not.