I have been searching for an answer to this but have not been successful.

DD-X is my favorite developer. However, I do not shoot and develop enough to use a 1 liter bottle within 3 months. Is there a way to tell if DD-X is still good, perhaps by looking at its color? Or I simply have to get rid of it some amount of time after opening it?

As additional information, I mainly shoot Delta 400 on 35mm/120 and print on Ilford RC/fiber paper

Thanks much for any information you can send my way.