Stop fertilizing for the winter, and definitely stop with the Dyna-Gro. It's really made for hydroponics and has lots of trace elements and IS ammonia based, so it could be salt build up, high levels of trace elements, or something else entirely, but let's eliminate known problems. Shouldn't fertilize in winter anyway, so this gives you some time to rinse that soil out well, and find a nice organic fertilizer that will help build some healthy living soil (seaweed emulsion is nice and less smelly than fish emulsion, which is also good. Winter color is a possibility, but those green veins make me think too much fetillizer (phosphate, mostly).
Let me know how this does; it'll be touch and go for a bit, but I think it will pull through.