FX-39 - minumum quantity of concentrate for consistency?

Hello All,

Sorry, another question...

... does anyone have an idea on the minimum quantity of Paterson/Adox FX39 concentrate that is required to consistenly and fully develop a roll of film (135 or 120) at the usual 1+9 dilution.

I know this has been covered numerous times for Rodinal and HC110, and I'm aware of the "official" minumums of 10ml and 6ml respectively... but I can find no discussion on FX39.

The reason I am asking - I have just bought myself a Jobo 1520 tank, which takes 250ml for a single roll of 136-36 film. This would mean using 25ml of FX39 concentrate. However, there are various quotes around that state that the minimum total volume of diluted developer (when made up from liquid concentrate) is anything up to 500ml per film.

I would quite like to develop two rolls of 135-36 films at once, and if 25ml of FX39 is not enough, I can't do that (if it's not consistent)!

I once asked this question to Paterson. They replied that 30ml concentrate is sufficient for one roll of 120-film.

I've done a bit more reading, and found the following in the FX39 data sheet provided by Paterson:

Diluted at 1+14 (e.g. 20ml makes 300ml) - useful when films with short development times are quoted. Extend development time by 50%. Diluted at 1+19 (e.g. 15ml makes 300ml) This provides a compensating developer....

Click to expand...

Now this suggests that perhaps 15ml is enough to develop a film... I suppose the only thing to do is to try it. In my Jobo 1520, it would be 25ml to make 250ml. I'd hope based on the absolute amounts noted above that 25ml would therefore be enough to develop the film normally.

Would continuous agitation exhaust the developer more quickly?