Seems like two problems. 1) sediment buildup 2) Plant Chlorosis. For the sediment buildup, I would get rid of the drip irrigation, not sure why people use drip in sandy soils, It would be better to use larger orifice sprinklers like impact sprinklers or spray. i know white sapote is very very sensitive to being hit by sprinklers. Then, if you still have buildup, physical filtration. The second is a little more tricky, I know a lot of people use the elemental sulfer, that seems plausible. Chemically treating your irrigation water seems like a waste of time and money when your soil is calcareous. You could amend your soil with biochar and/or clay to make it easier for plant roots to take up the elements they need, pH would be less important in this situation. Then the last option, but should be first, is to just increase overall biodiversity of plant roots/fungal relationships around your plant to make whatever nutrient your plant is missing (iron/mag) more bioavailable. I fixed a jackfruit nutrient issue just letting my weeds take over around the base of my tree.