First, this isn't meant to be mean or snippy, but buying products off the shelf in a box store is not generally going to give you any better results than a homeowner can get himself (thus eliminating the need for a professional) Probably 99% of box store products are homeowner grade, idiot friendly, "watered" down versions of what you should be using to perform a higher level of quality.
There are higher concentration based products available to contractors that will blow your socks off in time savings and results difference!
Secondly, why would you leave an oxalic product on the deck. The stuff causes health hazards - people walk on their decks barefooted and animals drink from puddles. You should be rinsing.
Third - just stay away from anything with Behr on the label. It will bite you in the long run. Most of us here have either gone that route or took advise and used a different road.
Celeste