Well I finally read a couple of small articles about ideal Ph and EC (Electrical Conductivity) for soil.
A Ph of 6.5 is ideal for nutrient absorption.
For soil, it turns out that a reading between 200 - 1200 microSiemens per centimeter (µS/cm) is ideal for the EC.
Well I flushed my potted mango plants with a lot of R.O. water and measured (with my Hanna pocket meter) the water that drained out the bottom. It turns out that I have been over-fertilizing. Some of my mango tree had readings of over 2000µS/cm and one with a reading of 3000µS/cm! Good golly! Lancetilla and Pickering had these type of readings. Now I need to flush out my plants completely for the next couple of weeks. Two of my trees had reading of about 800 micorsiemens which was great but their Ph was pretty high (over 7.5).
I am hoping to adjust my watering from now on and watch my plants.