Leaf issues

[b3rnd]

Hey guys,

I just spotted some leaf necrosis on my older plants. Any idea what it could be caused by?

I water when when the mix is dry. I fertilize once a week and I have a fan blowing. Temperatures fluctuate between 23 and 17 Celsius.
 
Edited to add: I grow in coir, and I recently switched to pre-buffered premium quality coir instead of the unbranded crap I was using before. I also ordered ferts that are specifically for that brand of coir, and I've been using it on the plants in the crappy coir as well. Could that be a factor?

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[Brewster]

LED Light burn..? 

 

[KevinThePepperhead]

Looks like light burn to me too.

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[b3rnd]

LED Light burn..? 

 
 

Looks like light burn to me too.

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I agree it kinda looks like sun scald, but they aren't directly under my lights. I just have one lamp and it's used for seedlings. These are in the periphery around the lamp. 
 
I thought I'd try to find people who posted about a problem that looks similar to mine. I couldn't find one before but I used a different search term and I found this topic. Looks almost identical and the conclusion seems to be overfertilization.

 

[PaulG]

Some that looks like leaf hopper damage, which
then goes into necrosis. Pics 1, 3 and 5.
I have a few plants with something similar this
season, and couldn't figure it out. Then, I saw a
leaf hopper on one plant and 'evicted' it. Haven't
had any more hoppers or spots  since then. 
 
Maybe just a coincidence?

 

[solid7]

You fertilize once a week...  that's a suspect statement.  How much, and what?

 

[b3rnd]

I use Cellmax Coco Grow, at the ratio described there. Should I dilute it more or fertilize less often?

 

[solid7]

I can't really tell how big your plants are, or what the recommended dosage is for a given plant size...