Response to Shelf life of MCM100

The problem in all cases is oxidation of the developing agents. The use of distilled water might help in reducing any dissolved oxygen in the solutions, as will less vigorous stirring during mixing. Also, Sodium Sulphite is more effective as an anti-oxidant than the Bisulphite.
You say you're using glass stoppered bottles. By this, I'm not sure whether you mean bottles with glass stoppers.
The standard tapered ground-glass laboratory stoppers aren't actually very good at excluding oxygen, unless they're greased with Apiazon or Silicone high-vaccuum grease. Try doing that, or changing to screw capped bottles with a decent neoprene gasket in them.

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