One of the keys to DIY developer mixing stock solutions that keep well is to take your distilled or reverse osmisis filtered water, and boil it in a good sized nearly full stainless steel pot with a lid that fits well before you use it to mix the chemistry. I boil gently for at least 10 minutes, and then turn off the heat and let it cool (usually overnight) without removing the lid. I decant into 4L glass jugs, and keep it on hand as the need to mix arises.

The boiling drives off a reasonable amount of the dissolved gasses.