Thanks cturner... I appreciate any help I can get.

The plants that have yellowed look otherwise healthy... no droop, curl, etc. I added a very, very small amount of coffee grinds to the yellowed plants just to give a very small dose of nitrogen. I know this will drop my ph slightly but I have a little wiggle room there to stay within the acceptable range.

So far as going to 18/6, the lowest amount of "daytime" lighting I've seen recommended by the seed vendors is 20/4 for these 60 day autos. I am at 24/0 now so dropping to 20/4 is something I probably should, and will, do.

The lights (400w HPS) are about 4' from the plants. I plan to move them closer when the plants start to show sex (about 2wks from now) or earlier if they look like they can handle it.

BTW, I re-calibrated my hygrometer and the humidity is stable at 50% temp 80%.

Thanks for dropping by and offering assistance. I appreciate it. Have a great day!

P.S. I should mention, The plants have not progressed to the point of the first pot change. So, the medium they are in now has no nutes... just peat, vermiculite, and pearlite.