Ok, just about the time I think I am starting to understand this, I screwed something up and I am now totally lost. I need help. Somewhere I really messed up and ruined 3 rolls of 120 film. I tried developing 3 rolls of Efke R25 120 film in a Jobo 2509 tank. I am using Arista Premium Liquid Film Developer. The mix ratio for this developer is 1:9. The 2509 tank has a capacity of 90 ounces to properly cover 3 reels of film. So I mixed 81 ounces of water and 9 ounces of film developer and proceeded to develop my film for 5 1/2 minutes, which is what the Freestyle database indicated for this combination. I use a nice little aquarium heater to maintain my solution temps close to 68 degrees. What came out the other end was totally and completely clear. There is nothing but clear film base left. So obviously something went wrong, but I am not sure what. It has been a very long time since I was in school, and I was certainly not a math whiz then, but I didn't think I was that bad. Guess I better think again. This was my first go with the Jobo tank and the Arista Premium Developer. All my previous attempts have been made using one reel in a small tank using a Rodinal solution mix that I copied from some article somewhere. Those previous attempts turned out successful, so I am obviously good at following simple directions. But, since this was a disaster, I am obviously not so good at photo developing problem solving on my own. Thanks very much for any help you can give and I would certainly appreciate formulas, or sources for those formulas, where I could expect to enter variables and come up with a correct result. In other words I would like to be able to play around and actually learn how to do this on my own.