Had used the HCL89 from the http://hcl89.byethost10.com site before. I had an issue with my grouts from my resale flat where the grouts were black due to dirt. Tried using the above product and it managed to turn back my grouts back to the natural white grouts.
Also tried to use the HCL89 on my kitchen backsplash tiles/grouts and it basically rejuvenated the backsplash tiles/grouts for me back to its original self
The HCL89 product seems to work much better than others that i have used before and seems to have to have solved the stained tiles and grouts problem for me
My 2 cents