What is the cause of this?

This was the oldest and largest leaf bunch on the plant and it was the first to turn yellow.
it lost its softness as it yellowed, and the leaf veins remained green.
also the plants leaves are a lighter color in green than ive usually seen.
the tips of the mirroring leaf bunch started to brown and curl up also.



i water every 1-2 days using a moisture meter to make sure its mostly dry beforehand.
under a 400watt hps 18/6
temps had been peaking at around 100, now they peak at around 90 (have an inline fan to implement which should drop the temp another 5 degrees or so)
humidity levels between 40-55 and i user a sprayer lightly one to two times a day to help raise humidity.

soil was in a quart size pot until i noticed the condition and transplanted it to some miracle grow 20-10-10 in a 3 gal pot

Looks like Potassium deficiency to me

do you think the new soil will be sufficient in that regard? its miracle grow over and under watering protection soil.

Yes it should be. Just keep the PH in check and you should be fine. She should get better in a few days if you just transplanted

thanks, ill keep an eye on it for a while.

some of the other leaves are yellowing slightly in the same fashion, but hopefully it will slow to a halt.