Eco Friendly Cleaning Solution
I suggest to stay with commercially available, read-made solutions. These products are thoroughly tested and certified.

They typically contain around 5% of various benzalkonium chlorides, such as N-Myristyl-N-benzyl-N,N-dimethylammonium chloride, as biocides.

UPDATE As far as the mildew is concerned: The orange ladybird (16 white spots) and the 22-spot ladybird apparently feed on mildew. If these two are naturally found in your region, get some. This is as eco-friendly as it can get to keep mildew in the garden close to a minumum.