weird problem Burn spots on 1 plant and not any others

View attachment 1721069Its actually a strong yellow color the pics dont do it justice

tomorrow im planning a res change

Room temps 70-75
Rh between40-51%
Ph 5.7
Tds 400
only one of my plants seem to have a big problem and strangly they SHOULD all be the same strain

Well I can tell you the white crust is calcium or lime from hard water.

that would be a decent assesement except i use R/o water and that spout has recently been cleaned

really i just want someone to tell me what causes spots like that in two days

If your using R/O you got me then not sure why you would have a white crust.........Whats the source of R/O?.....Because I thought I was getting good R/O water from walmart at one time then I tested ppm and it was at a 100 and with the same meter tested some local store R/O and it was 6-10ppm.

Check for tiny white bugs under the leaves. If you got them, use neem oil.

For your spot question I think since you use RO water you should raise your Cal/Mag. For me I had those using RO in soil using a cal mag supp. But then I switched back to well tap and Im still using Cal/mag and necro spots are no more.
I bet those leaves that have the ongoing spots will be dead and limp in a couple weeks.