2nd set True Leaves started curling down help.

Looking for some advice im a newbie grower but have been successful so Far till today but not to big of a deal just want to get opinions here is my set up!
I'm growing indica strain afghan big bud
24x48x68 tent
6" fan blowing lightly on plants
Inline air carbon filter
600w Full spectrum LED
And using hydroponic bucket system with air stone
Temps around 71-76 degrees
And humidity from 59-70 usually stays 65-70 once in a while it gets low to 59ish

Leaves on the first true set started curling down in one night. I did move the light down from 30" to 24" and put it back up to 30 incase thats the issue here is a few pics im running 3 plants the first pic is the yesterday and the second pic was today's and the other pics are the other two plants doing fine in exact same setup thanks in advance.

Cot-LEY-dons will fade then drop off over a 3-4 week period is natural

good luck

It was the true leave but I believe it was my light i moved it closer then when I moved it back up it straightened up.. thanks for the response though im surebi will be asking more questions as I go.