Some how Red knew he was the one I was going to reach out too... props to the homey REC as usual! That would work perfect for your situation Herb. Run it at half dose as I said your soil probably has some lime in it - if you don't see it respond, run it at full dose - by mid to late flower you'll probably need to run it full blast anyway if they're showing some issue now. It'll stop the progression within a day or two of watering. Also, I know I have some material from Muddy about foliar feeding for CalMag def, but I think it's more magnesium targeted..