Specialized Exterior Stain Remover for Stubborn Black House Stains

The user is dealing with stubborn black staining on their house exterior that a power wash couldn't remove, indicating a common and persistent problem for homeowners. This presents an opportunity for a specialized physical product: a highly effective, easy-to-apply (e.g., spray-on, brush-on) exterior cleaning solution specifically formulated to tackle tough black stains (likely mold, mildew, or algae) that resist standard cleaning methods. The fact that someone suggested 'crushed vitamin C tablets' indicates a gap in readily available, effective, and perhaps less aggressive solutions for homeowners. The product could focus on being homeowner-friendly, perhaps eco-conscious, and provide lasting results.