There are "one shot" developers like Ilfosol and Rodinol, which you use once and chuck out -- Much easier to start. Then there are things like D-76 which you can use over and over ading just a bit of time with each roll. The second type have capacities which the manufacturers publish on the bottle/envelope. I'd stick with one-shot to start, easier and reliable. If you want to do two rolls at once, maybe think about getting a bigger tank and using twice as much one- shot. Dean(posted 8369 days ago)