Hi
I have a concrete deck around my pool and it borders with shrubs and flower beds. Every year it gets dirty (blackish color) and I need to power-wash it. The concrete is porous looking with small granules on the surface.
Can I use any additive to the water in order to clean better? There are coping stones around the pool and the grade is right, but I'm concerned about effecting the pool water and also the flowers and shrubs around.

I'm considering coating the surface with something in order to prevent the on going dirt accumulation. Any recommendations? If needed I can post pics.