I do aero and aero/fog, with great results.

As Tiny pointed out, it could be just stained from nutes or additives.

I would not use H2O2, hydrogen peroxide, not because of "beneifcal bacteria", which is not needed in aero or aero/fog but because it is not compatible with some nutrient lines.

Look for a product that is chloramine based, it has all the pathogen killing power of hydrogen peroxide, but is much safer for the plant and won't screw with the nutrients.

Dutch Master's product called "Zone" is such a product.

OM