Leaf issues

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?


Verstuurd vanaf mijn SM-G930F met Tapatalk
Brewster said:
LED Light burn..? 
KevinThePepperhead said:
Looks like light burn to me too.

Sent from my SM-G975U1 using Tapatalk
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.
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?
I can't really tell how big your plants are, or what the recommended dosage is for a given plant size...