Rick:
Good points, but keep in mind that the roof materials manufacturers ' main concern is making and selling roof materials. They recommend chlorine because that's how it's always been done and they know it works.
Very few of the manufacturers invest a whole lot of research and development $ in how to clean their products in a safer manner. Some shingle manufacturers have done it only because of warranty claims arising from their fillers that actually promote algae growth - so now they have come up with AR shingles - but the tile manufacturers, in general, don't seem to care at all.
I have worked with extensively with several of these manufacturers and they all know that there are better ways than chlorine, but it's not a front-burner issue for them. If you look at the tech bulletins, you'll see that they are 9 years old - and they are exactly the same as the ones published in 1980 (with the exception of the sentence regarding algae resistant products). There's not much recent R&D going on there.
A good example: I had one of these guys acknowledge that safer chemical cleaning is better for the shingles and will help extend the life of the shingle. Then he asked me to explain how this was going to help him sell more shingles.
Also:
I you call a few of the shingle manufacturers and ask them for an alternative to chlorine, most of them will tell you that Home Depot has products that will clean the shingles safely. These are generally sodium hydroxide based products.
Sodium Hydroxide is actually a very common cleaner found in everything from oven cleaners to toothpaste. The levels of caustic are really what determines whether it will clean without doing damage. A 1-2% level of Sodium Hydroxide in your finished mix will clean the roof effectively and will not damage the roof if rinsed of properly. Chances are, you'll do much more damage to the shingle by rinsing than you will by using the sodium hydroxide on it.
Hope this helps!
