It looks like from the pics that just maybe your water is "HARD" causing your soil to lose its 7 ph.I'm going through almost the same exact problem w/my plants.After mis-diagnosing my plants many many times,Finally decided to look at my H2O.Does that shit resemble rust a little bit????? When i 1st noticed that shit on my plants I, like you started to try to diagnose the problem.1st i thought that is was nute burn,because the tips of my leaves were kind of drying up,turnin a gold color type & getting crispy.After flushing that crap out of them,I started to get "gold or rusty spots"in the middle of my leaves but the tips started to look better.Then all of a sudden all hell broke out w/my plants.Unknown to me that my ph that origianlly was @ 6.3 had jumped to @ 9 or so.That tester that u brought back to K-mart was the one that i used.Eventhough they're not known for great accuracy their good enough to get an idea where your ph is.When your ph goes up or down it blocks some nutes from going where they need to be.I now usedistilled water for my girls. hope this helps.
