Removing oak tannin stains from patio?

Been rather silly and stained patio of my rented house that I'm about to move out of.
Chopped down a dead oak tree a few months ago in my old house and cut up the trunk into 10 pieces to keep for future use. We then just stuck them on the patio (not wanting to ruin the grass) but now I've come to move them got lots of big brown stains which I presume is the tannin from the fresh oak.

I've tried washing with various household bleaches and cleaning products and they have made the stains a lot lighter but still quite visible. I'm hoping that if I do the same every day for a while the stains will eventually go. Anybody got any experience of this and ideas as to a better solution?

 

Perhaps:

http://www.agwoodcare.co.uk/gbu0-prodshow/oxalic_acid.html

Or brick cleaner acid (hydrocloric)

 

Thanks for the reply Pro Gard. Two days on and stains almost gone with household bleach apart from some stubborn bits. Might have to get some of that stuff to deal with the last remains.

 

Pro-what about that creosote stuff-how do I get that off. It has to work very quickly-if hubby gets back and sees it fur will fly

 

I seem to remember struggling with that one in the past. Time to pop out and get some new paving slabs?

 

creosote will need household amonia to shift it, a generouse slug in boiling water with fairy liquid, scrub it.