epictetus

The cedar shake on a friend's house (currently under construction) was treated with a sealant and it became a little too dark, so he had the contractor who applied the sealant lighten it up. They sprayed it with citralic acid, which I've just learned is a mixture of oxalic and citric acids and it did lighten the wood up but it caused a black stain to appear around some the galvanized nails in the shake. The nails were electroplated galvanized as opposed to "hot dipped." Any suggestions as to why this happened and how he should go about fixing it? Thanks.