yeah it looks like fert burn, basically u gotta always keep track of what your doing.if u did this +this and this hapends but you do this+ this +this and this negative shit happends but your first 2 adjustments didnt cause any problems then the third one is your factor. flush your soil with plain ph balanced water. i would bet that u wont even need any nutes for some time because of the soil your using.but im not really a soil guy and have never used mg.good luck