Rusty spots on leaves

Hello every one I have this problem with one of my plants. There is these rusty looking spots on some of the fan leaves .It literally looks like someone smeared rust on it. I tried rubbing the rust off to see if it is rust fungus. But it didn't come off. I red that it will smear off on you finger if its fungus. The other reason i dont think its rust fugus is because the RH in Arizona is any where from 10% - 35% RH normally . I'm feeding it fox farm trio fertilizer . But I cut out big grow and very little tiger bloom. Mostly big bloom i feed it. One thing I did differently was I gave it 1 ml per gallon of Cal mag (used half of a gallon). Ive done alot of research on this and cant find anything really helpful. There has to be someone that could tell me what this is. Thanks Jay

Another reason why I don't think its RF is its not spreading to the other plants

Ph issue

I checked my ph. the fist time and it was 7 I did it a second time and it was 6 but that one was with distilled water . I'm not sure which one is right. I also tested my tap water with a soil test kit and it was 7.