The Internet's Finest Tropical Fruit Discussion Forum!"All discussion content within the forum reflects the views of the individual participants and does not necessarily represent the views held by the Tropical Fruit Forum as an organization."
Manganese deficiency.
What are you watering with? Well water? Maybe sacrifice the sod for mangoes.
Others could speak to this better, but I think that it takes a good while for the leaves to show improvement, after you apply minerals. I'm not even sure that the older leaves will always improve.
Have you sprayed lately, such as with oil or soap? It looks as though something settled on the lower parts, dips, of the leaves.