Hey, I haven't been on the forum in years, but I am a nursery grower at a tc nursery in central FL. Looks like Cueva copper soap (Certis) is the same as Grotto (OHP), which I use as a weekly preventative in the greenhouse on my alocasias, anthuriums, bananas, kava, and other plants that suffer from foliar pathogens such as anthracnose, pseudomonas, xanthosomas, phytophthora, etc.
Souther Ag sells it in 1 gallon form as well, not sure if you can find this chemistry in smaller volumes, except in sample sizes.
As far as the rates, Grotto calls for 0.5 to 2.0 gallons per 100 gallons. I've had success using it @ 1gal/100 gal. The label states it can be tank mixed with wettable or flowable sulfur, so that's a plus! The main issue with copper is to treat it like an insecticide, only put it out when the temps are below 85 and will stay below 85 degrees until the product dries on the leaves. Like all copper chemistries, don't get in in your eye!
I also use potassium bicarbonate (Mil Stop from BioWorks) to treat for anthracnose and powdery mildew in the greenhouse. I haven't tried it on mango trees yet, but plan on trialing it on future flower panicles. Most of my trees are going in the ground this year.