I don't think this is nute burn...

I've got a sneaking suspicion you're dealing with a calcium excess.... it can often manifest itself as nute burn but it ALSO comes with dark brown blotches such as your first photo is showing... Is the top of your soil getting "crusty"??? I think I can also see signs of some droop starting on some of your leaves ... and a definite curling up of the leaf tips.. the combination of these elements would definitely point to a calcium overload. I would do a flush in any event. You KNOW something is wrong and this is the best way to kind of "reset the clock" as it were. And try to get the pH down to about 6.2-6.3 ... add in your Big Bloom nutes in your final gallon of the flush and let her dry out. (You can actually increase the Big Bloom significantly if you want... might obviate the need for calmag... generally, I use about 9tsps/gallon of Big Bloom at this stage and, instead of Grow Big, I use 1-2 tsp of Tiger Bloom). Going forward, if you feel she needs calmag, only give it to her once a week max.... she should be just fine! Good luck!