While doing a roofing restoration service, I have encountered the following problem. A house built 10 years ago, is then finished. With the ceramic tile. In many areas, it was covered with black or greenish tarnish/dirt. The roof area was about 120sqm. I was asked what was the best way to clean it so that it looked aesthetically pleasing.
My first answer is: if you have to clean a tile so quickly, it means that it was really not well made. So it would be better to sell the old tile and put a completely new one. That is why I ALWAYS recommend choosing decent manufacturers, e.g. Braas.
However, to actually answer the question. How to clean such a roof? I recommend a simple washer. Then installing copper nets by the ridge tiles because when it rains copper ions destroy algae.
James Horst
Roof Restoration Cranbourne