Just started flowering - leaves curling and twisting

Hey everyone I just switched my lights from HPS 18/6 to MH 12/12. Everything was going fine for a few days and now all of a sudden ive noticed the leaves are starting to cup up, some of the tips are twisting and the edges are curling up. The humidity is 25-35%. The MH is about 18"-21" away from the plants and I have a pretty good fan blowing between the light and the plants. I have a humidifier as well but I'm having trouble getting the humidity above 40%. I fed one plant out of the 3 I have because the leaves were turning pale green. The leaves came back to normal color but now all 3 have curling and twisting leaves. Let me know what u guys think. I would hate to lose these now. Thanks again

What is your heat?
The MH lamp, will burn hotter....
I have tested my 100 watt MH to my 100 watt HPS...
I have a digital Therm pointer...
The MH lamp ran close to 380 f degrees, right at lamp...
The HPS ran 290 at lamp... so the area, around lamp that used to be 290 f degrees, is now a hundred degrees hotter....
Fans do not "Cool" the air... They just move it...
Hows the exhaust fan? Can you get the hot air out? Or does it now build up?
I had to install AC window units for this very reason...
Even though ambient air temp is now 65 degrees... that MH warms and dries the air...
Maybe go back to your HPS until the heat and lack of humidity is fixed...

I have a similar issue sides of leaves curling up and twisting. My humidity is 20-30%, is that in fact my problem?