Schefflera- leaves turning black and dropping
I would like some advice on how to save my schefflera. I've had it for 2 months, it is about 4 feet tall, in a 16" diameter pot. The nursery repotted it before I brought it home as they thought it was a bit root bound. It is planted in a plastic pot that sits inside a ceramic pot (the edge of the plastic pot rests on the lip of the ceramic pot so it does not sit in a saucer). It is in a corner next to northeast-facing french doors that get a fair amount of indirect light. I've watered it when dry, it has had new growth and hasn't lost a leaf. I rotate it slightly to expose all sides to the light.
So, two weeks ago I left for a week to attend a conference. Because it was going to be hot I pulled down the translucent shades on the french doors and all of the other windows in the room. The air conditioner was turned to 80 degrees and I watered it one last time (about 2 quarts).
I returned home to find blackened and green leaves on the floor. It sheds leaves every day, sometimes black and sometimes green. I have posted a photo here.
I talked to the nursery,showed them photos and they thought it was the lack of light and that it dried out and was "shocked." The leaves seem to be dropping only from the back of the plant (facing the corner).
I bought a water meter which indicated it was dry and gave it water ( 5 cups) very slowly (1 cup every 1-2 hours). Yesterday it lost only one leaf. Today it lost 11, 7 were black or partially black and 4 were green.
I hope I can still save it, any suggestions would be greatly appreciated.