Stop mildew/algae build-up on old vinyl siding?

[Terri Pour-Rastegar]

I need to figure out how to stop this mildew or algae stuff that shows up on one of my rental house's older vinyl siding.

I end up having to pressure-wash this crud off at least yearly, but it really needs it 2-3 times per year! It's really ugly. What can I do to prevent it from coming back all the time?

The siding is otherwise in excellent condition.

[Account Closed]

Zinc on the roof.

You can buy Moss B Gone and sprinkle on the roof. You can buy special zinc strips to put on the roof, or you can place galvenized chicken wire along the ridgeline.