One plant having issues

Hi,
I am having a strange issue with only one plant out of four. The leafs are curling up along the edges and all the tips are turning brown. The other three plants are looking fine and don't currently show any issues. Photo
s 1 thru 3 are of the problem plant and photo 4 is the same strain right next to it. These plants are all from seed and it is currently day 53 from pop.
Photo 1



Photo 2



Photo 3



Photo 4 - Same Strain right next to the problem plant.



I am growing indoor with daytime temps running around 81 lights on, 76 lights off. Humidity is 60%. Co2 is 500 ppm.

3 Gallon fabric pots with coco and been watering DTW every other day 1/2 gallon per pot with Jack's 321 full strength.

Lighting is a total of 8 3500k cxb3590's at 50 watts each at about 12" above the plants. Shows to be 600 Ppfd.

Any help or suggestions would be greatly appreciated.

Thanks in advance

Sounds like heat stress, possible nute burn?... but without pics hard to tell. I dont see any pics?

Pictures should be showing now

Looks like heat stress and overwatering.. possibly light or nute burn

You adding cal mag?
What is ppm ec of nutrients when mixed?


Edit What kind of water you using?

Starting with RO water and Mixing Jack's 321 at the standard ratio. The really odd thing is that it is only this one plant. The other three all look good.

If it were me, I'd mix up @ 3 gallons of new feed, being sure it's pH'd correctly, and I'd slowly pour it through that plant, with the idea of resetting your medium. There is something in that pot, your plant is not liking...most likely salt build up. A 1/2 gallon of feed every other day, in a 3 gallon pot, when running coco isn't much....you may want to consider increasing this. Good luck.

That is light burn. The cobs are too close. My opinion. My belief

Sounds good, I will do both.
Ill raise the lights for a while and also flush out that pot real good. I have been mixing each 1/2 gallon separately so its possible that I blew the measurements on one feeding.

Thanks for the advice