Just a general note.
Our atmosphere is acidic and oxidizing due to the CO2 and O2 in it. Any alkaline solution left out in the open will react with CO2 and form a salt while decreasing in pH. Any reducing solution left out in the air will oxidize. This goes for the solids as well as the solutions I might add.
Therefore, developer, which is an alkaline solution of reductants goes bad when exposed to air. The CO2 makes it more acidic and the O2 oxidizes the reducing agents including HQ, Metol, Phenidone, Glycin and etc.