I think it's a potassium issue as well - but your pH is in a good spot (IF you measure it yourself and do not rely on what your nutes say they maintain!) .. If you have a pH pen, double check what you're giving your ladies and also check the pH of the runoff... that will tell you what is actually in the soil as far as pH is concerned... it SHOULD be between 6.0 and 6.5 ... anything lower than 6.0 will bring on a whole host of problems - neither calcium nor potassium can be absorbed by the plant if the pH is below 6.0 when growing in soil...
I use Langbeinite once a month, sprinkling 1T on top of my soil so it leaches into the soil a little bit every time I water or add nutes... the NPK of it is 0-0-22 and it's brilliant at keeping both potassium and calcium and magnesium levels where they should be... as long as a good pH level is maintained... if it's not, it's useless as is calmag...
Good luck!