Heat / light stress or a deficiency?

[Kush]

Strain is Tangelo Rapido by Barney's farm.
Grown in soil that has a pH of 7.0
Grown under screw-in off the shelf LED lights.
Temperature in the box was high for a few days (31 degrees Celsius) and humidity was and still is low (35-40%).
The plant was fed a single dose of brown Kristalon about 3 weeks ago. Has been fed pure tap water ever since.
It was growing Okay up until the problem appeared. Plant got damage on some of its leaves. Here is what the damaged leaves look like (photo below).

What is this? Heat/light stress? Nute burn? A deficiency?
Thanks!

 

[razor]

Strain is Tangelo Rapido by Barney's farm.
Grown in soil that has a pH of 7.0
Grown under screw-in off the shelf LED lights.
Temperature in the box was high for a few days (31 degrees Celsius) and humidity was and still is low (35-40%).
The plant was fed a single dose of brown Kristalon about 3 weeks ago. Has been fed pure tap water ever since.
It was growing Okay up until the problem appeared. Plant got damage on some of its leaves. Here is what the damaged leaves look like (photo below).

What is this? Heat/light stress? Nute burn? A deficiency?
Thanks!

View attachment 837689

I'd say calm mag I had same problem with my kush .issue she auto ?

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[razor]

I'd say calm mag I had same problem with my kush .issue she auto ?

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What nuets are you useing ? And I'm veg or flower ?

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[woody]

Can you post a pic of the full plant under natural light. And give a little more detail on feeding and plants age.
Looks like a phosphorus deficiency though

 

[Kush]

I'd say calm mag I had same problem with my kush .issue she auto ?

She is an autoflowering strain but she did not autoflower. I am now growing her like a photoperiod plant, under 12/12 light schedule.

What nuets are you useing ? And I'm veg or flower ?

She is in flower. I fed her a single dose of brown Kristalon several weeks ago.

Can you post a pic of the full plant under natural light. And give a little more detail on feeding and plants age.
Looks like a phosphorus deficiency though

Here is a relatively recent photo of the plant under 3000K LEDs. I am afraid that I cannot provide a photo under natural light - she lives in a grow box that is placed in a dark room.
She is ~9 weeks old from sprout.

 

[KonopCh]

Looks like P deficiency.

Plant also look little overwatered and she's clawing (high N).

 

[Kush]

Alright, if this is Phosphorus deficiency, then would feeding the plant a dose of brown Kristalon cure it?
Here is the NPK ratio of brown Kristalon: 3:11:38
It also contains Mg and S.

 

[Heavily Medicated]

I am not familiar with Kristalon, but you do have a P def and although the numbers could be a bit different, I would give her a shot of the feed. The large K component would be a little more appropriate for later bloom, but if you have nothing else feed her the Kristalon.

 

[Kush]

I am not familiar with Kristalon, but you do have a P def and although the numbers could be a bit different, I would give her a shot of the feed. The large K component would be a little more appropriate for later bloom, but if you have nothing else feed her the Kristalon.

It turned out that I have another fertilizer at home which has a NPK ratio of 4:6:6. I wonder if that other fertilizer would be better for treating the P deficiency than the 3:11:38 Kristalon???

4:6:6 or 3:11:38 This is the big dilemma that I am facing.

 

[Kush]

OK guys, I had no time to wait for your reply in this thread, because my plant is dying, so I took care of business.
I read online that just giving the plant more Phosphorus won't do much to cure a P deficiency - you have to mess with the pH as well.
So, what I did was I lowered the pH of my soil from 7.0 down to 6.0, using water with some vinegar in it.
I also put a teaspoon of brown Kristalon in the water, as well as 7,5 ml of another blooming fertilizer, in order to raise the P content in the soil.
Let's see if all this will help or not. The plant reacts very quickly to the P deficiency and loses leaves like crazy, so I really hope that it would be just as fast to react to the cure.