Hard to tell under HPS, try grabbing pics with the light off under the flash. The very first thing I do whenever seeing a deficiency is to calibrate my PH pen and check the runoff PH to make sure I'm not locking nutrients out.
The pics from the 16th are not mg deficiency though IMO. Definitely could be mg def in the latest pics, but a mg deficiency typically starts around the out perimeter of the leaf and works its way in with a pattern of discoloration that appears different than N deficiency. The latest pics do appear as if they could potentially be heat stress given the location of the stress on the leaf. Just my two pennies.
I suggest either start using cal mag every other watering for the first half of flower, mix garden lime into the soil at transplant or top dress after transplant. One of those three and at least you'll know the plant has it when it needs it, I usually use 1 Tblsn per gallon of growing medium of lime. When I first started growing in FFOF my plants would ask for nitrogen, cal and mag EVERY cycle at 2-4 weeks until I figured it out. I've used both CalMag and lime and both work well. I really like the simplicity and use of cal mag because it also provides a small N boost all in one and I can just continue with flowering nutes. The downside is that I prefer to grow mostly organically and calmag smells like toilet bowl cleaner lol. I tend to use a little of both usually.
Another tip for temps.... Frequently people will just throw a thermo in the tent where ever and monitor their temps thinking they're fine... What is important to monitor is the temps directly at the plant canopy. A thermo on a bamboo stick stuffed in the substrate and placed in the middle of the canopy at cola height will give you accurate readings for temps that are very important. They will tell you what adjustments are needed and will also insure that you get the healthiest plant tops and densest colas come harvest time
EDIT: I just looked at your last pics and the temps said 86 which is pretty high. I see some eagle clawing too which is another indicator of transpiration being effected by temps.
For some troubleshooting, a closer investigation can help you dial it in.