Hi garyb,

...bluey green sludge was coating the inside of the tubes
I'm not one to argue with a chemist, but this also sounds like some leaks I have seen where brass and/or copper were present at the leak.

Were the pinhole leaks developing from the inside or outside of the tubes? Did you cut out an affected area to see if the corrosion site was internal?

Has anyone checked the CIP washing fluid for the coils to see if the cleaner is compatible with the grade of aluminum used in the coil?