I have one of those Paterson System 4 tanks. It takes 2 reels using 35mm, and one reel for 120. I looked on the tank and on the instructions, and it says how much developer to use w/ each, but not for 2 reels of 35mm. Do I simply double the amount for one 35mm reel? The reason I ask is that I developed 2 rolls of 35mm in it recently, and some of the negs have a darker line down the middle (horizontally). I had the film in two cameras, one w/ a vertically running shutter, and the other w/ a horizontal one. Can't remember which was first. I did put just 17 oz in it because I had been developing 120 before that and forgot to change the amounts. The tank calls for 10oz when using one 35mm reel. Maybe I should have put 20 oz in it?