I recently switched to flowering, under a 400w hps from CFL. I’m less than a week in and have noticed fan leaves are turning brown and looking not so great. The new growth is looking fine but I’m trying to figure out if this is normal or another problem. I have two clones, SD x LH and Blueberry headband. I’m getting temperatures ~80 degrees give or take 2 degrees, and humidity is 38%-45%. At night, it cools to 66 degrees and humidity drops (dry dry climate) to about 25-30%. I have been feeding with neptunes harvest 2-4-1 and growing in organic soil. Any ideas? I have an exhaust, 80 cfm with a vent somewhat connected to the hood fo the HPS. Additionally running two fans and a humidifier. Any ideas or is this normal as the plant switches to flower?
It could be the change in lights. The new growth is use to it, where the old growth is not use to the increased heat and intensity. Just a thought.
Heat burn.Give them a good watering no ferts and move your light up for a couple of days.Can also use a small oscillating fan to move your plants around…Anytime you move from flourescent or led to HPS always raise your light for a few days as the hps is hotter.
Heat stress downward curl on leaves as check your PH what’s it at . totally agree with @SmknCanuck
Thank you! That is a feeling I had but wasn’t sure if it was something more dire. I raised it to about 19" and gave them a good watering. Will update!
You may want to go higher than that, 2 foot anyway
and this caused:
Back the light off. Next time try a gradual switch of the light spectra/intensity over a few days-week.
Plants sense light differently than we do & taking, for example, a clone out of indoor lighting into full sun mid-day & it will possibly-probably die.
I’ve done it a bunch. 
sorry if i’m bein’ an asshole - blame my neighbors