[jimcarry]

I think the more agitation the better the solution should appear as if it is boiling .
The darkening from the acid im not to sure about .
But the yellow chromate not adhering is a preparation issue the piece needs to be clean polished
and free from all grease and oil.
Preparation of the parts you are plating is the most important step .
The best finish you start with is the best finish you will end up with !