I am sorry to say that you have a bunch of different compounded problems. The first big mistake is the use of Fox Farm soil. You have to be very careful with that stuff because it has an unbalanced supply of nutes in the soil, so even when adding recommended doses, it will burn your plant (I found that out the hard way). Second, you may have a calcium/magnesium deficiency but it is probably being caused by excess nitrogen blocking it, and not necessarily a lack there of. Little to no nitrogen is needed this late in flowering and I have found that even when flushing Fox Farm soil, the problem is not easily remedied. I would not suggest foliar feeding unless it is with the lights out, otherwise you are going to further compound the other problems (heat stress, moisture, poor circulation). I tried trimming/pruning my fan leaves and it only sent the plant further into shock. Anything done to a plant including flushing is shock to a plant and it needs time to recover. Switching back and forth between different remedies is only going to help drive urself crazy and won't pinpoint the problem. I know you don't wanna hear this while your plant is "dying" but you have to try one thing at a time and give it (the plant) a chance to correct itself. I am going through the exact same thing and one of the first problems I was able to pin-point and fix was air circulation. I thought it was everything from deficiences, to bugs, to just being cursed...lol. This not only happened to my plants that were flowering, but to two plants during veg, so I don't think your doing that bad. The only thing that is telling me is that the problem has to be environmental or a problem with the ph/nutes. I will keep you posted, but try not to panic to much (if that's possible). Trust, I thought abt throwing all my plants out the window yesterday.