In 54% green Phosphoric Acid- what contaminant would cause purple scale to form inside pipes & components?

We have purple scale plugging up stainless steel piping and pressure regulator valves in a system flowing pure 54% green Phosphoric Acid. Never seen this in 13 years of operation. I suspect another chemical that was in a tanker truck or transfer hose previously may have contaminated our bulk tank during the last acid delivery. Has anyone seen this before? Scale formation is light purple in color and chips off fairly easily with a screwdriver, and it's plating out everywhere in the system. Please help!