http://www.mistral.ie/details.php?code=R61202kg in 25litres produces quite a strong bleaching mix that will kill algae etc but unlike SH bleach does not remove the colour from the wood nearly as much. It also completely biodegrades in just a few hours so is kinder to the environment. It takes about 15 minutes to properly dissolve in hot water, and as always wear the appropriate ppe.
This is the main chem in "vanish oxy action",.. my mrs keeps nicking mine for the washing machine! (No,. not an april fool joke,. deadly serious!)