Bottoms of leaves brown/drying out

[SentencedToBurn]

Hi guys
 
I have 10 DWC peppers in my greenhouse, the temperatures are between 15C (60F) and 30C (85F). Humidity is over 90% at night and is about 55-60% at day time.
 
They get plenty of sun, and I run my budget grow LEDs for about 6 hours at night to help out with reduced light hours. All DWC buckets are 10 liters (about 2.5 gallons I think?), all run airstones, all get completely flushed about every 4 weeks, and get topped up every 3-4 days. All buckets have foil covering the sides so there is 0 algae, all roots on all plants are perfectly white.
 
9 plants are doing great, all flowering, some already starting to grow fruit, one (Aji Amarillo) started getting brown curled leaves, where the bottoms are pretty much dry. Could this be some kind of bacterial leaf spot? I disenfected the hell out of my greenhouse earlier in the season though just in case.
 
Here is a close up of the leaf in question. There were some that were a lot worse which I've trimmed off, should've taken a pic of them.

 
No other plants have this at all, all are healthy as.
 
Any suggestions would be greatly appreciated.
 
 
Thank you
 
 

 

[SentencedToBurn]

Actually I found a thread here: http://thehotpepper.com/topic/20372-my-pepper-leaves-have-brown-and-torn-edges-and-holes/ which seems that this could be fert burn. I'll empty half the bucket tomorrow morning and will refill the rest with plain water and will see whether that works or not.