I'm suprised to hear that, my experience has been that beadblasted surfaces dye the easiest.
I use glass beads only, 150 -200 mesh (fine) what's important is they are used on aluminum only. The presence of steel particles or other metals will cause anodizing defects, but this doesn't sound like your case. You must have an effective oil trap in your air line, the presence of compressor oil on the work can cause what you describe. Another possibility is wrong cathode placement, what happens if you reverse the orientation of the work in your tank? Did the reverse side anodizing look OK before you started beadblasting?
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