Hey Dave, not to steal anyone's thunder
but I have a very similar problem...and it's driving me, well it's driving me! I have a GH and the catts are up front and sunny. I fertilize everytime I water with either 20-14-13 or 11-35-15, urea-free with minor elements. Mostly I use the 20-14-13 and will switch over to the other soon...I have lots of phals so I try to promote leaf growth now. I do have a 70% shade cloth on the GH...maybe this is my problem. The temps here in Michigan have been 50/60 nite, 70+days