I use both Naval Jelly and the liquid form depending on what I'm doing. The Jelly is just to keep the acid in place while it does it's job.
It seems that the white, chalky residue happens when I leave the acid on too long. The chalky stuff is kind of hard to remove and a real hassle. I'm thinking 2 minutes is about right, but 5 minutes is too long.
I've also seen a green residue when I've done a light wipe of the liquid and forgotten to wipe it back off. Not sure what's happening in this case.
