I agree. Cal mag all the way... purple stems can be genetics, but brown purple spots on leaves is cal mag...Cal/mag probably
You can, flush for 3 minutes... buy some cal/mag. After 2.5weeks, and the problem has stopped, result to removing damaged leaves if the problem doesnt spread and cal/mag works... only new growth should have no symptoms, only old growth. Old growth wont heal...Should I just flush it?