Confirm diagnosis please

I suspect this might be a Mg deficiency but I wanted to run it by you all. My grow has been trouble free thus far until I saw this tonight right before lights out. What you will see in the picture is only on 4 branches of a fairly large plant. The issue is on the top most fan leaves only. She is 27 days into flower.

The only thing that has changed recently is that I did a reservoir change 2 1/2 days ago and chose to only use RO water instead of 80% RO and 20% tap water. My tap water is well water and has gotten really bad lately.

I probably just under estimated how much Cal Mag to add but I'm hoping you guys can confirm!

Thanks in advance,

HDS

Calcium brotato chip .... check your calmag bottle and see if there is a recommendation dose for heavier issues. My GH calmag says 1tsp for general application and 2tsp for MAINTENANCE.

Top side brown spots usually fit the calcium deficiency profile . It looks fairly early , easy to correct.

Budzbuddha said:

Top side brown spots usually fit the calcium deficiency profile . It looks fairly early , easy to correct.

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Thank you kind sir.

Hot Diggity Sog said:

Thank you kind sir.

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Anytime ... keep it green brother ...

Budzbuddha said:

Anytime ... keep it green brother ...

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One final question:

Should I expect the brown spots to heal or just stop seeing them spread?

No healing .... it is necrotic tissue ( dead brown ) ....
You are only trying to stop spread .
Plant WILL THINK it can repair , but it is damaged.

Budzbuddha said:

No healing .... it is necrotic tissue ( dead brown ) ....
You are only trying to stop spread .
Plant WILL THINK it can repair , but it is damaged.

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Got it!