check the pictures
thanks
It doesn’t look like you’re adding Mg. Coco is known for creating Mg deficiency as well. It looks like it could be beginning stages of Mg deficiency. Get some epsom salts and put a teaspoon in your water. See if it helps. I have never had a deficiency such as Magnesium or Calcium because I supplement. Epsom salts and make some calcium acetate (powdered egg shells reacted with vinegar until pH =7). Homemade CalMag that is cheap.