Water filter the issue ?

I posted a while back about plant problems and was getting rust like spots on the leaves. Fixed it with epsom salts and continue to add 1/4 teaspoon to gallon of water for feeding and last night i noticed the spots have came back on some of the leaves up top. Could my pur water filter be the issue ? I was using rain water before but cant use it anymore. I was reading somewhere that water filters may filter out calcium and magnesium ? I always keep my ph around 6.0 to 6.2. She is growing in coco and starting to pre flower but im sure the leaves are not supposed to do that
 
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