What has changed at Gatsby's house? What is the reason for these changes?
I will assume that you are referring to the time after Gatsby and Daisy meet and start spending time together. The changes the take place in Gatsby's house are that everything quiets down. He no longer has his enormous and outrageous parties because the whole point of these parties was that one day Daisy would wander in. This is why Gatsby never really participated in the happenings of his parties. They were for her. Now that he has found her, or she has found him, he let the workers go so there wouldn't be any talk or rumors. It is unclear if he is worried about people speaking about him and his business or if it is about word of her being with him getting back to Tom.