I will take a closer look at the developer tomorrow when I go to the darkroom.(posted 8412 days ago)I don't think that you will get so much air in the solution when you're stirring - you're not whipping the solution.
You can use a tall form beaker to get a smaller surface that's exposed to air. Even better is to use an Erlenmeyer Flask and a magnetic stirrer. Then you can use a stopper on the flask. But that would be expensive. Using glass beads as stirrers is another option.
Sorry for my bad english.
Patric, Sweden.