I thought it was galvanized

Hey, I’m Mike Holland from Dothan AL and my company name is Swift Water Surface Cleaners.
Quick overview of what I did. A realtor who owns an multi unit office complex asked me to clean the walkways and only part of the roof. The roof has about 3’ high of high angle metal all the way around the building. That was all she wanted cleaned. All of the concrete work was knocked out and whatever was on top or along the side of the walk was washed back about 2’. Next was the roof. I thought it was galvanized, even when you got up close to it, it still looked like galvanized metal. I am running a 20% dsi and was using a mix of 2.5gal sh 5oz Elemonator and water. This didn’t lighten the mold or loosen the dirt. So get up close and change tips to start moving the stains and dirt. The roof was white. It has never been cleaned in the 20 plus years its been there. There are pine trees and pecan trees all around. So if you have dealt with pecan trees you know how messy they are. After letting the mix set to the point it was drying in spots and rewetting it and dwelling for more time it still would not come off without using high pressure and heat. I even went straight from a jug of SH to the dsi and let that set for 5 minutes. It was a little easier to remove but still needed high pressure and heat to get it off.
Needless to say it took about 6hrs to clean about 800sqft. Anyone have a suggestion on what works on these kind of stains that can get done with low pressure or this is just how it is?

You can always direct apply to get a hotter mix (12v, pump sprayer or brush an’ bucket). You can also use a stronger surfactant, just test for negative reaction before going to town. Typical roof mix is at least 1/3 sh so you can’t achieve that concentration downstreaming (can get close when xjetting but that can be risky).