Random yellowing started today?

[Gnomex26]

Hey guys, so before work i checked water and realized i needed to water, but when i came home 10 hours later i realized some of my very healthy plants have started blotchy yellowing to a few leaves underneath being full yellow. I am freaking out cause i have spent so much time to have issues now, first grow. I will give pictures below, do you think its a nitrogen thing or hopefully a heat thing cause i have an A/C unit in the mail, coming tomorrow.Thank you for any help, i dont want to lose my first real grow.

 

[Lowrider72]

Your letting them dry a bit too much and it affects the roots.
You get yellow leaves around bottom if plant yeah?
I get this occassionally if I mess up, water at least when the pot is half the weight of when its just been watered, its a good guage, keep you safe.
Damage is done, watch new growth.