I'll take a couple of guesses but thats really all they are....guesses.

1. Maybe need some CalMag.
2. fert building up in the medium. I've had this issue both in hydrotn AND higromite rocks but I use a drip system so...as I said.....guess. But the nute buildup in my medium REALLY played havoc with my plants.


MVP....what kind of ppm meter do you use?