Recently purchased dieffenbachia having trouble.

I just recently bought this from Aldi. Maybe two or three weeks ago. It felt moist when I bought it, I let it dry out, and have watered it once since I brought it home. It was big and beautiful, and now its getting quite a few yellowed leaves. I removed about 4 or 5 of them so far. Im also seeing curling and browning on the tips of some leaves. It's still showing some new growth despite all of this. It is directly under a NE facing window and about 10 feet from an E facing window. This room ranges from 70 to 74 degrees. Please help me keep this beauty alive!