I am experimenting with a 4x5 view camera and have bought a tank to develop the negatives. I am mixing up a gallon of D76 developer. It will be in two half gallon containers. The developer data sheet shows 1 gallon will do 16 sheets of 8x10 cut film. I am doing 4x5 negatives so I would get about 64 negatives give or take a few. However I only will be processing 6 to 9 negatives at a time and my tank uses about 55 oz. So I intend to return the used developer to the half gallon bottle between my batches of negatives. Since film comes in 50 pc. boxes, the plan is to run 25 sheets per half gallon. The question is does anyone know the expected developer shelf life, once I start reusing the developer, assuming I can squeeze the air out of the half gallon bottles.