anyone tell me what caused this?

i personally think its under watering. You say you use a 16 oz cup. Does that mean all they get is a 16 oz cups worth of water each watering?

I say flush them and get some bloom nutes. Something high in p or k if you just wnat some generic nutes from the store. I use fox farms grow big, tiger bloom and big bloom and love them. Make sure when you flush you use 2 times the container size of the plants of phed water.

Than I suggest you water atleast 1 gallon of water when they need to be watered. That way you majke sure they get enough water. Over watering is not a to much water at watering issue. It is watering to often that you need to aviod. I think youir caution has caused you problems.

Do the flush and get some nutes and see how she does. if by the next watering she has not imporved we know the issue is some where else. And get a soil meter. Use that to determine when to water. Its cheap and easy way to keep a good water schedule for each plant.

Good luck

and to the low humidity. No worries. Mine is low like 25-30 percent. I clone 100 percent success with no dome in that same humidity.

well yesterday i watered with molasses and nutes, today they are looking better, the lowest set of leaves that was affected on the 1 plant is normal and the next set up is starting to come back.

i also filled a pan with water and put in there to raise the humidity, im still unable to get it over 40%