Leaf end turning brownish yellow in SOIL

[fallss]

So they are 3 weeks old, I am having to put them under 12/12 because of time constraints. I began this yesterday. Today is the first time I'm noticing the issue. They are in a mixture of ocean forest and light warrior soil. the pH is 7 and temperature between 76-85 with humidity of 50%.

the strain is either blue mystic OR super lemon haze, I don't remember which pot it is.

here are pics

 

[fallss]

any assistance guys?

 

[Droopy Dog]

Looks like the beginning of nute burn to me.

DD

 

[Hogdady]

any assistance guys?

How to Ask for Grow Support

 

[greenishman]

hey check out my pics, i seem to have the same problem as you do...!
at first i thought it was because i'm not adjusting PH and have a nute lockout problem, but now i think it could be also a nute burn problem...!? although i have used a fert, i didn't used a lot of it really. still don't know what is the exact problem and how to fix it...
please let me know if you find something, i'll do the same!
cheers