CLEANING STATIONARY SCREENS:

I have an unheated three-season porch on the north (shady)
side of my home. This porch has screen sliders all around and glass floor to
ceiling.

The screens get a green mildew on them from our MI

weather
patterns (I am presuming it is mildew but it could be mold I guess.) due to our
ever changing cold, damp and humid climate here in SW Michigan and being an
unheated porch.

I need ideas to remove this mildew from these screens. IF
these screen could be easily removed I would spray, hose and dry in the hot
sunshine but these screens do not come out. I have a very expensive custom river
rock pebble flooring on the floor of this porch so I cannot just spray a
product power wash and hose it off while the screen are in place vertically.

I have a power washer but this river rock floor is
impermeable and any water that is sprayed on it, runs through it to the cement base
and that means a change of mold between the river rock and the cement beneath,
so that won’t work either. Any chemicals might change the color where it drops
so that is not an option either.

My husband tried spraying them with an organic plant based cleaning
spray with towels/old blankets underneath to capture any overspray and that did
not work.

IDEAS for cleaning mildew off my screen anyone?