If you divide the made-up developer into smaller full stoppered bottle quantities it should be good for about 12 months or more. Good bottles and stoppers are hard to come by, though. Dark glass bottles with plastic screw caps and neoprene washers under the cap are ideal. Beware of cardboard washers, even if they're plastic or foil coated, they'll let air in. Visit your local Pharmacist and see if they're throwing out any large medicine bottles.(posted 8979 days ago)As a rough-and-ready guide, if the developer shows any more than a pale straw colour, don't use it, it's begun to oxidise. One final tip, exhaling (not blowing) into the bottle as you close it will displace a lot of the oxygen from the air gap.