Help! Brown spots on serrated leaf tips

[MackMcMacMac]

Hi experts!

I have a young auto/fem growing in a space bucket that I topped a week ago. Her new tops look good, but I noticed one fan leaf has brown tips on the leaf serrations. I'm concerned! Can you tell me what (if anything) I need to add to the water to combat this problem before it gets worse?

Strain: auto/fem Tutankhamon (mostly sativa) from Pyramid
Age: 22 days from sprouting
Medium: FoxFarms Ocean Forest in 3-gallon felt pot inside a 5-gallon bucket (indoor grow)
Nutes: None yet, just plain water that reads pH 6 (but last time I watered, I forgot to test the runoff)
Lights: 4x100w (4x23w actual power draw) "daylight" CFLs on 18/6 schedule ~6 inches from tops
Fans: 2x8cm "pc" fans for intake, no exhaust yet (but the bucket has 4 available 8cm fans)
Avg daily temp (in bucket): 76° F
Avg daily RH (in bucket): 60%

I see the brown spots mostly on the leaf in the 9:00 position, but there's a spot on the opposite leaf too. You might need to zoom in to see them.

Any help/advice would be much appreciated!

Love,
Mack

 

[MackMcMacMac]

The problem is getting worse. I photograph my plants almost every day, and I noticed the edges starting to turn about 1 week after I transplanted her into the 3 gal pot from the solo cup, though I'm using soil from the same bag. The photo above was taken at age 22 days from sprouting, which was 9 days after the transplant.

Here she is today, age 28 days.

I've tried to diagnose her from the graphics I found on this site, but I can't figure out whether she has a deficiency or an excess. I doubt it's excess, or she'd have shown nute burn long before she was 3 weeks old, right? Thinking it was a calcium deficiency, I gave her some CaliMagic on 27 Sept, but that didn't seem to make any difference. In fact, the next morning, she looked worse.

Now, I'm leaning toward it being a P or K deficiency. Since I haven't fed her any nutes before the problem showed up, that's on the short list. In desperation, I flushed her with about 30 pints of water. Runoff measured pH 6. Then I fed her 0-10-10 bloom nutes, since she is starting to make baby buds on the tops.

I'm so new at this, IDK! (I have one other bag-seed plant growing in the same soil who showed none of these problems, and she's 10 weeks old and making pretty buds for me. This is the extent of my experience in growing MJ.)

Any advice would be much appreciated!!

 

[MackMcMacMac]

Mystery solved: Classic potassium deficiency. Added 0-10-10 bloom nutes and problem went away.

 

[dj1714]

Glad to hear you solved it Mack. I'm sure this will help others.

 

[BTzGrow]

Help! I think I might be in a similar situation.

My brother who also grows and is in the know much more than myself feels it's a Calcium or Magnesium deficiency. I have been adding a mix of Epson Salt at 1 teaspoon for quart of water to both foliage spray and into the soil. Any assistance and or confirmation of my problem would be really helpful. I'm currently trimming and pruning off any affected leaves.