With my Jobo 1520 tank, it is possible to process two rolls of 35mm film or 120 film at the same time, in 500ml of developer. I've tried this occasionally, but not always with good results. Will 500ml of a developer always be sufficient to handle two rolls? (Some developer instructions say don't re-use after processing one roll, which seems to imply it can't handle two.) Would I need to use a different -- i.e., increased -- agitation with two reels in the tank (for 35mm film) or two rolls of film on one reel (with 120 film)? I'm using mainly DDX and Perceptol, by the way. Would be grateful for any suggestions.