A white buildup has formed on stainless steel parts after soaking in NaOH with aluminium pieces How to remove?

The stainless steel tubes have a 5mm internal diameter so i would like to use a chemical to clean them rather than brushing or sanding. Originally i thought the white substance was dried NaOH but HCl or water have not removed it. Now i am thinking that it must be some kind of aluminium deposit. Please help by identifying what may have formed or even better how to get rid of it