The problem is growing everyday progressing up the leaf towards the stem. Here is a big picture of old foliage being affected by it. I water my 6 month old mango every 5-7 days. It grows in a 68F-75F grow tent and gets 12 hours of light from my 2000W grow light everyday. I run 2 fans on opposite sides of the tent that run 24/7 that oscillate. I added 3 tablespoons of BGI Citrus Fertilizer about 3-4 weeks ago. Every watering, I water until it starts to drain out of the bottom of the 8" pot. I use tap water. I live in Washington USA in King County.
Am I not watering enough? Am I watering too much? Is it too much fertilizer? Should I use different water for watering? I'm lost at what the problem is and my other mango tree lost all its leaves from the same issue!
I recently bought this moisture meter to see the moisture level and pH of my soil. It says my soil is around 7.0 - 7.3 pH. I watered this mango tree on Sunday evening and it says for right now, Wednesday evening, the soil is 2 on the moisture scale (dry). I don't know if I want to trust this meter though because it seems to be really cheap and the soil near the drainage hole seems to be a little moist still.