Cleaning Brick

I wasn't exactly sure where to place this post, but, the white bricks around my rose garden have both what looks like algae, and water stains, and just misc stains from being outdoors.
I've tried soap and water with a little bleach, several types of my wife's house cleaning products, finally, muriatic acid, and a strong industrial cleaner from the local hardware store.
Nothing seems to work, and these bricks are not inexpensive, so I can hardly just go down and purchase new ones to replace these that don't look that great.
Thank you.