I haven't come across that claim. Can you share the source or quote? BAC water is the usual choice for mixing GHK-Cu. Sterile PBS works but has no preservative so it isn't suitable for storing the mixed peptide over time. Only a strong chelator would pull the copper away from GHK, and BAC water isn't one.
I've heard that BAC water makes GHK-Cu lose its copper properties that matter for the benefits. Does anyone know if it really changes things enough that I should switch to PBS instead?