If you are trying to be all "organic", use seaweed in all your waterings and sprays. This will provide some Copper and Zinc, etc. Some kinds of rock dusts would also help. Some chelated products and some complexed products are also labeled for use in organic production.
I don't see any indication of Mango Bacterial Black Spot (MBBS).
[Bacterial black spots on other plants are usually other species of bacteria, which tend to be host specific, so we should not leave off the word "mango" in the name.]