Aluminum Oxide on Porous Exterior

I believe the exterior material is an engineered limestone or simply a finished concrete. The sconces in the picture are aluminum. The black run off under them is what i assume to be aluminum oxide. Does anyone know what the magic solution for this will be. Im leaning towards an acid based upon my experience with both copper and iron oxide. There are alot of these sconces 3 stories high…so instead of experimenting, which will inevitably happen on the first one, I would love to get some tried and true advice on this one. All comments are much appreciated.

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Eacochem. Call them.

We have had excellent results with F9 on that type of stain. If you have some, the proper solution is 1 part water to 2 parts F9. Do a test section. Spray F9 and let it dwell for 20-30 seconds. Pressure wash off. Call me 855-803-1133 with any questions.