Indoor setup with few small orage brown spots and light green leaves

Hello all. I need some indoor diagnostic help. These spots look to me like a manganese deficiency. I am positive it is not nute burn, infestation or light damage. The spots are very few right now, and I wants to fix it before a significant problem arises. There is a pic of one of the plants. Also, is the light color is due to a nitrogen deficiency? These are Afgooey clones and the leaves never got that ultra dark color. Any ideas? Sorry to post the question here. I never see great advice in the problems area.

looks like low humidity.

dude your plants are about to bud correct? your lighting is at about 12 hours? your plants are suffering from low PH...... when they bud they like...5.7 most bottled water is 7......check your PH.

I haven't moved into bud lighting yet, but I am about a week away. I have been neglecting the PH, I'll buy a meter. Any cheap way to manipulate ph safely?

any hydroponic store will carry ph up and ph down. Very cheap no more than 5 bucks a bottle.