So in the past it had a iron and/or copper deficiency, causing dieback and plenty of offshoots. I buried bits of copper and steel and it responded almost immediately. Now there are bleached spots on some older leaves and the younger leaves are pretty light in general. I think it might even have a zinc or potassium deficiency. I will leave some pictures to help you identify the problem.
I would recomend a soil test to know with certainty whats happening in your soil. Sometimes to much of certian micro and macro nutrients can give the symptoms of deficiency, and without testing to determine exactly whats happening, the problem can go from bad to worse. This means even with pinpointing the nutrient symptom, you still need to determine whats the exact cause trough testing. Unfortunately putting chuncks of refined iron and copper in your soil, complications the diagnosis, as it could easily be applied to heavily, or have other advertise side effects that alter pH, or stress the soil biome effecting nutrient uptake or utilization. Thats why it's always best to use amendments that occure naturally or are at least frequently used for agriculture applications, which also have known safe rates for general and spacific applications.
Thats my best suggestion, baised on the circumstances, and will get you difinitive answers to solve the problem, without further unnecessary or unwanted complications, that could further compromise the health of your tree.
That first picture looks like normal wear and tear that you see on any plant this time of year. Life in the wild is hard, and any number of things may be abusing those leaves.
Is the tree in a pot? If so, some of what appears to be happening is salt damage, which is usually more acute in a potted plant than one grown directly in the ground. Most municipal water has a degree of salt in it due to the chlorine they use as well as naturally occurring salts in many water sources. If you are using chemical fertilizers, that's a big salt source. Salt builds up in the soil, particularly with potted plants. When you see burnt tips of leaves, that's a good indicator of salt damage.
I would flush the pot with a 2-minute heavy watering, so that water runs right out the bottom of the pot for a while. That'll wash a lot of the salt through the soil. Mangos are trees so they really don't want to be contained in a pot. Can you get it in the ground and let the poor tap root run free and go wild? If not, perhaps consider re-potting it in something much larger, and give it a big dose of well-made compost. That would solve most concerns about nutrient deficiency.
Best of luck.
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