I use promix out of the bag with a scoop of dry ferts once in awhile.
when i first pour it into a bucket and transplant I kick it to feel the weight of a dry bucket and add about1/4 of the container volume of water to it at once.
I look for a spot of run off in the drain holes underneath/on the sides. If none appears I add till it does.
I dont add water again until the bucket/container feels dry again..... then I repeat^ for a flawless finish
they dont react this way from that light change btw. you need better dirt/more aeration at minimum