Burnt tips! Help!

Hey guys, been going through my first grow and I’m about 5 weeks into flowering and I am seeing burnt tips curling up everywhere! I have been dealing with the problem since mid veg, I figured it was nitrogen burn from the miracle gro I stupidly plantEd them in. So I flushed multiple times untill runoff was basically clear, but I am still seeing burnt tips, I checked my water ph it seems fine, but my water is pretty hard I’m realizing and reads at 320-380 tds. Could it be the hard water? or maybe I haven’t got all the nutes out of the soil ( because of the time release nutes) or am I way off and is it a deficiency of some sort ? Please and thanks guys
 

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