I use a 1+9 solution in a tank that only holds 225ml of solution for developing single 36 exposure/35mm films. This is 22.5ml of concentrate, and gives identical results to those I get from a 450ml double tank, and a 900ml quad tank, loaded with either 35mm or 120m or 220 film. I get good, consistent, easy printing negative densities at Ilford's recommended times with just 22.5ml per film, (or 45ml for 120/220) so I suspect that even this is nowhere near the lower limit.(posted 8354 days ago)