I don't for a minute think I'm risking important negatives by developing them at 1:75 or 1:100 with less than 10ml of stock Rodinal solution, because I have been doing so for 20 years with absolutely no problem. My developing times and agitation techniques seem to compensate for the reduced developer activity. I always mix film developers in distilled water, so there is no problem with variations in water quality.(posted 8285 days ago)I have been careful to state Agfa's recommendations, but I also do not hesitate to state the results of my own experience. I think what Agfa is really saying is that if you use their developing times, you must use a minimum of 10 ml stock solution--but I've never found their times or their recommended exposure indexes to be particularly useful.
I use a small tank that holds 2 35mm reels or one 120 reel. I mix 500ml of working solution, of which I use approximately 425 ml. I have an old 120 spool that I have clipped to about 1/2 inch in height which I wedge into the top of the tank so the 120 reel doesn't slide up and down during agitation. I agitate for 10 seconds (about 4 inversions) once every minute.