Your ingoing water ph is too low. For a peat-based medium, a ph of 6.3 to 6.8 is optimal for proper nutrient uptake.

Since you just transplanted them, they are possibly getting used to the fresh nutrients, too.

Cannabis needs a wet-dry cycle, but don't overdo it in either direction. Overwatered, they'll droop and the leaves get all puffy. Kinda like a quilted effect.

Without burning the plants, keep the lamp as close as possible. If the back of your hand can stand the heat for one minute, the ladies will be fine. My 400w HPS batwing was around 14-18 inches, if memory serves me. Not much lower than yours, but makes a big difference.
Rusty Trichome Reviewed by Rusty Trichome on . what is happening to my plant after I changed to 12/12 lighting... I don't understand, it was all fine at first but then one of them started acting weird... during the 12 hours of darkness the plant seems to be okay because when I come in to turn on the light the leafs are all normal and pretty but then an hour or so after the lights are on they start to droop, I don't understand because it's not too hot, I have managed to keep the temperature about the same since they seedlings... on the pictures you will see the difference, the first picture is right after Rating: 5