Hey John, on a metal roof start with a 1% mix first add 1 gal of green wash that amount will dwell longer on the roof. For most metal roofs 2% should be a max. If you make your mix at 4% that will be way to strong and might take the green off . Pecan stains, leaf, acorn, can be tough to get out. But on a metal surface it should come off. Bleach Wash rinse. Hope this helps.

Agreed, never put 4% on a metal roof. 2% max. AC

Thanks for the input, I should have remembered that about the metal roof but that is why I posted. Thanks for stopping me from making a huge mistake.

I have looked around for a Bleach Wash mixture to rinse the roof with but haven't been able to find one. I do remember that the roof should be rinsed and bleached washed. In the past I have used the hose end sprayer but this time I need to put it through the pump. Thanks for the advice.