Just checked runoff ph is 6.5 ppm 150x10. The ppm going in is 550-650 & ph in is usually 5.6-5.8
1500ppm coming out in the runoff is high! Your ppm going in should be higher than your measured runoff. Your is backwards and your having a lock out of nutrient. Your sodium leves are rising and dropping your pH to an acidic range.
What I initially thought was not a problem, now is. I believe what your seeing is a Phosphorus deficiency. Your going to have to flush out the built up sodium in the coco. General rule is 3 times the volume of container the plant is in. So 10 gallon pot, you'd pour 30 gallons of plain water that has be pH stabilized at 6.5
Test the pH and ppm at the end. If your in range 550-650ppm don't fertilize. If your below, run 650ppm
@6.5 pH until you get 1/3 runoff.
Alternate when you fertilize. Every 3 days, otherwise just add pH stabilized water.
Feed, water, water. Feed