I used a small amount to clean some white stones that had turned green with algae. I placed the stones in a bucket of water, added about 50ml of oxi pure and left them overnight. The next morning most of the green had gone. I added another 50ml and left them for the rest of the day, and when I went back they were all clean!
I have now added a small amount to the fountain water to keep them clean. I am so pleased I won't have to scrub the stones clean ever again!