Powerwash with Bleach "should have" alleviated any mold and mildew. I "survived" Chemistry, I forget what algae is and all that.
Muric Acid is used on brick I know to "bring out the brick" once laid. On Vinyl siding , I have used diluted Simple Green to clean, as have others. Some of these Cleaners are really "harsh" and have butanyl-something or another in them. Simple Green does not have whatever that harsh chemical...
I clean a lot with Baking Soda and Baking Soda and Vinegar. Does not scratch Fiberglass, countertops, etc.
I'm wondering if Baking Soda sprinkled on the ground would alter [neutralize ?] the soil and conditions for Algae?
Moat? I'd save that idea to have Zoning Changes Made so Neighbors could not park in the yard.
"Hello Police, Yeah El T here, Cletus done come home and backed into his Moat again, send a wrecker, but don't forget to issue a citation - that goes against HOA...backing into the Moat. Used to parking in the yard...yep, yep, same fella with the Shark in the window..."