Please help diagnose: Light stress?

[AceOfClubs]

Two of my four plants are developing curled leaves, (primarily the new growth), as well as burnt tips and somewhat slow growth. I should also mention one of the two is very lanky.
I can't decide whether it's nutrient burn or light stress (or possibly something else). Im leaning towards light stress because I've only gave them one very small dose of root booster after the first transplant.
These plants are 3 1/2 weeks old. 12-14 inches under 600 watt metal halide, 20 hours of light.
What could be the issue? Thanks in advance

(This is my first time growing)

 

[MrFortwenty]

Taco leaves are generally an indication that it's too hot. Either from your light or the environment itself

 

[Blew Hiller]

You should def up-pot them into larger containers...that alone might solve the issue. What are you average temps? They look stretchy, and that might also be due to a small root ball. More soil gives the plant larger roots, which yields bigger plants that are more accommodating to temp fluctuations. Otherwise leaves look ok.

 

[Blew Hiller]

Oh, and

 

[MickFoster]

Have those plants been under a 600w MH the whole time? It looks like you had them in a window for sunlight because of the stretch.

 

[AceOfClubs]

You should def up-pot them into larger containers...that alone might solve the issue. What are you average temps? They look stretchy, and that might also be due to a small root ball. More soil gives the plant larger roots, which yields bigger plants that are more accommodating to temp fluctuations. Otherwise leaves look ok.

Temp is 28°C inside the tent. I will repot them in larger containers tonight, thanks

 

[AceOfClubs]

Have those plants been under a 600w MH the whole time? It looks like you had them in a window for sunlight because of the stretch.

No they haven't been in a window, besides, there isn't much sun here in Canada right now lol.
I've had them under a 75watt grow light for a week before putting them under 300 watt metal halide for the second week and they have been under 600 watts since then

 

[Blew Hiller]

Temp is 28°C inside the tent. I will repot them in larger containers tonight, thanks

28C is perfect.

 

[Blew Hiller]

I've had them under a 75watt grow light for a week before putting them under 300 watt metal halide for the second week and they have been under 600 watts since then

Probably why the leaves taco'd...that's a steep light curve for the leaves to adapt to...repot and keep growing...new leaves will be fine.