What is this?

Whats affected will not recover. And calmag may not help. You need to balance the cal and mag at about a 3 to 1 ratio. My guess is your tap water has plenty of calcium and you are just a bit out of balance. I would add 1/4 tsp of epsom salts per gallon of water to help bring the ratio of calcium to magnesium closer to what it should be.

Often times deficiency symptoms are caused by an excess of that nute. The plant really can't take more, and locks it out. So adding more just makes things worse. The way most deficiencies get fixed is a flush and then just re-giving the proper nutes. Calmag is really useful in hydro + r/o setups, but otherwise is not needed in excess. 2% calcium and 0.5% magnesium in the feed plus calcium in the tapwater is about perfect for soil. In hempy, I'd guess you'll only need an additional 0.2-0.6 ml of calmag through your rootzone every week.
As far as I know LED doesn't require more calmag. LGC seems to confirm my thoughts on that. If you have some info otherwise, please share. This is the first I'm hearing of spectrum type affecting nute uptake.

@Alexander Supertramp @Kush Knight ok thanks, I will pick up epsom salts today. I will flush everything and then up the nutrients to 700 and add the 1/4 tsp of the epsom.

Really really appreciate the help guys! Need healthy plants to make the RSO for my father in law. Plus found a filled 5lb tank of co2 at the local canals liquor store for $70 just need to get the regulator!