what could be happening?

I am in my 12/12 cycle for my plants and i noticed today that the tips on about 2 leaves are a yellowish color anyone kno what this could be, i have given them liquified worm poo for nitrogen and have given them some water, what else can it be?

if your tips are yellowish i would raise the light a little bit, sounds like they are starting to burn.

even on the ones that aren't that close to the light? the ones that are the right under the light are fine?

but i shale raise them a little

Thanks