Cleaning White Tile Roofs

I went to clean my first white tile roof a couple weeks ago and went about it as usual. Instead of coming clean, however, the surface turned brown and slimy. This hasn’t happened with any other color of tile. It wasn’t going to come clean without some kind of water pressure. Is there something I’m missing?

You might want to post this question over on the RCIA forum…lots of FL guys there who do nothing but roof cleaning.

That’s a good idea. Thanks!