Leaves curling up

[athos]

-Problem: I have some upper leaves curling up, like a taco effect. This has happened once two weeks ago around day 16 from seed, which lasted for 2 or 3 days until I transplanted form 16 oz cup to 2 liter pots. It's important to mention that this it's only present in 1 of 2 plants, same strain and age. The plant affected has been its 2 liter pot for 10 days. Could it be due been rootbound?
-Medium/grow method: soil, BIOBIZZ Allmix
-Feed and supplements used: So far none, just plain water.
-Water source: Tap water. Very soft. EC/PPM it's consistently 0,04 EC/20 PPM, haven't meassured pH
-Strain and age World of Seeds Colombian Gold non auto feminized seeds.
-Climate: lights on temperatures range from 23C to 26C (73F to 79F). Lights off they go as low as 17C or 63F. RH ranged between 40% and 60%
- Light used: Screw led bulbs 6 * 10 watts; 18/6 light cycle, distance to canopy is 7 inches.
-Additional info: 1 day this time, last time 3 days.

--Pictures

 

[MrGreen]

How often do you water

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[athos]

I water once when trasplanting, around 7 days later the soil is dry, I water again and 2 or 3 days later It's trasplant day again.

 

[namvet25]

Cupping of leaves is caused by heat stress or from lights being too close.Try moving lights up to 12 inches and see if that helps.

 

[athos]

Thanks for your quick answers. After all it was due been root bound, just as I suspected.