First, the obvious, are you sure you are getting air bells (bubble marks)?(posted 8780 days ago)Second, how are you adding the developer? The best way is to have the tank full of developer in the dark with the top off. Once you get the reels loaded, just drop them in the tank and then put the top on.
Have you tried a wetting agent? You could add a SMALL amount of Photo Flo or Edwal LFN to the developer.
ANd as others have asked, what about your water? I would try some mixed purely with distilled water (for both mixing the powder and for diluting the stock). This will remove that variable.