I pretended to play Song Madness for Chu Tiange in front of my parents. Which episode is it?

If I remember correctly, it should be that after the first conflict between Chu and ozone, they agreed on a duel time, and then they played CD on the piano in their room, but they were just exercising themselves. Chu's father and mother thought it was a heavenly song, and they kept praising it.

Because I was not sure, I went to check it again, and it was true. 17 episode is conflict, and 18 episode is piano loading.