I have come across a product that is designed to be applied to a roof and not rinsed.
It's called Roof-a-Cide. It doesn't produce results immediately, but it will remove the algea over the course of about 6-10 weeks (depending on the amount of rain) and it will inhibit new growth for up to five year - although it's only waranteed for two.
I find any product that does not produce immediate visable results for the customer is a hard sell. It is difficult to tell them that I am going to spray this miracle chemical on your roof, you will pay me now, and in 6-10 weeks you might notice a change...
Almost every other roof in Houston looks like its been through a black rain storm. Only those selling thier homes even care about the roof appearance. I am now using an M5 X-Jet and testing ratios with chems for roof results. Nothing has worked to even make a noticable difference so far.
I would like to know some specifics from those who have seen immediate results.
Chemical
% concentration
X-Jet proportioner color for 4GPM
Where to get the Chem.
% concentration when it hits the roof
Dwell time
If multi-concoction volume and % of each ingredient in 5 gal bucket
THis would really help.
Money is not an issue - I will buy anything just to have a base line to work from, to be able to say, OK this will get me the results I want on a black roof.
Sory for the long post but this roof thing is apparently VERY frustrating for a LOT of people and seems to take up a lot of room on these BB's. Too many different concoctions. We need ONE GOOD CHEMIST to figure out what works as a standard on asphalt shingles that appear black - and won't damage the roof material - and that does not require risking our lives climbing around on 60 degree pitch roofs in 100 degree temp's.