What's this?

Anyone know what this is? I am thinking cal/mag but I am not sure.

Anyone?

I'll take a stab, but I'm no expert. Hopefully someone else jumps in to help. Looking at those purple stems in your 2nd and 3rd picture, I suspect you have a Phosphorous issue in addition to needing CalMag. You may have a root ph problem if you are feeding them phosphorous. Here's a clip from Grow Weed Easy summarizing the symptoms.
------------
A cannabis phosphorus deficiency usually appears with some or all of the following symptoms:

• usually affects the lower and older leaves of the plant
• leaves darken (turning a dark green, blue or grayish color) and may appear shiny
• leaves may start turning yellow if the phosphorus deficiency is left untreated, or if the deficiency is combined with other nutrients deficiencies and/or pH problems.
• leaves get bronze, purple or brown spots and splotches
• leaves thicken and may feel dry or stiff
• stems sometimes turn bright red or purple, but not always

Phosphorus deficiencies in the vegetative stage usually appear at the bottom of the plant on some of the oldest leaves, and will progressively climb up the plant if left unchecked.

The progression of a cannabis phosphorus deficiency



Cannabis plants tend to love phosphorus in the flowering/budding stage and it is unlikely for a cannabis plant to get too much phosphorus using standard nutrients formulated for a flowering plant like cannabis. Nearly all flowering nutrients will come with an abundance of phosphorus for your plants. So if you're seeing a cannabis phosphorus deficiency while using standard cannabis nutrients, chances are you actually have a root pH problem (explained below in the solution section)!

Source. http://www.growweedeasy.com/phosphorus-deficiency-cannabis

i would recommend providing more information so that others can help to diagnose your problem. What soil are you growing in? What nutrients are you giving them. What ph is your water? The more you can give up front, the better your answers will be. Good luck!

I'm in canna professional plus soil. 8 gal airpot, following the canna feeding schedule at half strength, water is phd to about 6.5. Temps and humidity are where they should be

The strain is mango haze. Someone told be a shouldn't be feeding her at all which I dissmissed since I am in a pretty light soil( how is she supposed to get her food)