Our patio is built from bricks set on crushed limestone. We have a problem with a dark discoloration on the bricks. Many of them are discolored with a dark material- I would guess this is mildew, mold, or just the moss starting to grow. The patio faces east, and the odd part of this is, that much of it is in sunlight for a good part of the day.

4 years ago, we used a pressure washer and applied bleach to it and really cleaned it up. We don't want to use the same approach again,mainly because we don't want all of that water near our foundation, and the bleach couldn't be good for the two huge Canadian Hemlocks plants next to the patio where the runoff flows.

Is there anything we could use that would safely remove the discoloration? It isn't a thick moss growth or anything- mostly the stained dark look. The only thing I can think of is to fill a pump sprayer with white vinegar, and spray the whole patio with the vinegar and then let it sit for a day or so. Not sure if this would affect the Hemlocks, though. Would I rinse the vinegar after a day, or just let it stay? (not sure if I am on the right track or not with my idea) Thanks to anyone who can help.