That's true, I was confused on the EC/ppm issue. But that has nothing to do with accurate diagnosis of plant leaf discoloration. Truth be told, I never took the time to understand better what EC and ppm really are and what I knew of it was what I learned from others in forums like this. They were wrong too. EC/ppm and understanding plant discoloration are completely different things.
I've seen mag deficiency with my own eyes and what's posted in this thread isn't mag def. Please don't make inappropriate comparisons trying to make someone look bad. When it came to EC/ppm I should have kept quiet because I don't use these methods as I'm not a hydro grower. I prefer soil even though it takes longer. Hydro has variables to it that I don't have time to watch over.
How about the OP use your solution, adding mag was it?, and we'll see what happens. If more than one thing is changed, we'll never really know what the problem is.