as far as I know Patio Cleaner is a mild acid, which eats away at dirt and grime. This is fine on patios as they are concrete or slabs. Decking is wooden and therefore the patio cleaner may destroy the wood. Use a powerwasher.
There is one available thats specialy designed for decking:- "Jeyes decking cleaner" it kills algae, mildew as well as givving it a good clean up. I think its about �5.00 for a 2 ltr bottle.