One gallon is a really small rez....that right there will make things very hard to keep stable and in balance etc etc....

Please update about the roots....I'd like to see what happens there.

Yes do pull your lights back if you spray the Serenade. I pulled mine back for about 4 hours after I sprayed one tiime and it was NOT long enough. Now I go for a full 24 hours post spray and haven't had a problem with that length of time.

Your humidity is a large key in mold and fungus (you mentioned you live in a dry area) so finding out what that is would be good if you can. But stressed out or unhealthy plants will also be more susceptible to disease. I had some white rhinos that developed mold in a few spots due to being generally unhealthy (fert build up probs) even though my humidity was in the thirties (which is where you want.)

Good Luck!!