I'm confused about your procedures. Do I have this right?
You are:
- plating
- cleaning w/acetone
- drying
- acid bright dip
- drying
Why the acetone/dry step? I don't know what affect it might have, but there's no need for it.
Are you using brightened electrolyte? Are you chromating? Unprotected zinc will oxidize (white rust), and the excess temperature (130º is too high) will accelerate that.
Sean