I would guess something else is causing the ill symptoms that your tree is seeing, did you overwater or not have adequate drainage? I dont think that mix should have that strong of a negative effect on your tree.

Over watering might be the cause but I don't think so because I have a Mallika mango in a container side by side that I water the same time. But I didn't spray the Mallika, because the powdery mildew wasn't severe. Currently its leaves are healthy. I did have a guava tree in the same location that lost all its leaves a couple weeks ago but I think that was from shock, but those leaves are coming back now. Hopefully my Nam Doc leaves come back.

I can't remember ever seeing powdery mildew on mango leaves. I have seen it on the flowers though. Did the tree come with the powdery mildew or did you cause it? I think that your homemade powdery mildew remedy may be the culprit for the curling and dropping leaves. Keep your tree watered and fertilized and leave it along. Maybe hit it with a copper spray here and there. No need to become creative with new sprays. It usually leads to problems.

Guava tree in a pot losing all of its leaves? I think a lack of water may be the problem. Are your plants getting watered adequately?

Also, do you have a picture of the mild powdery mildew on your Mallika tree? I would be helpful to see it.