I recently used gutter zap on some concrete before I used my surface cleaner and noticed it was bubbling and turning red before going over with my surface cleaner. My first thought was that I had accidentally put muriatic acid in the pump instead but confirmed it was gutter zap. In any case the water pooled after rinsing the surface thoroughly and after it dried I think it left a stain on the concrete that I cannot get off. I say might because I don’t remember a stain being there before. Can anyone help out with this? And if did cause that stain, other than a grinding wheel, any ideas for how to remove the stain? Pressure and a wire brush have done very little.