The difference between erhu and guzheng?

There is no essential difference between the two for the melody score itself, but formally I think there are mainly the following two differences:

1, the erhu score mainly presents a single line of melody, mostly a single line of sheet music (the exception is the repertoire); and the guzheng in addition to a single part can also play two parts or multiple parts of the melody, so you can often see the score of the polyphonic part.

2, the instrument score is often added above the notes of the left and right hand fingering, playing markers (stringed instruments such as the erhu's right hand technique is mainly bowing). The fingering notation is very different for different instruments. The following two illustrations are for the subject's reference:

Erhu common notation markings

Guzheng common fingering notation

There are many examples of the form of the sheet music for the two specific instruments on the Internet, and the following two sheet music are for reference, and you can see the difference:

There are also sheet music of the erhu + guzheng together, and you can see the two types of fingering, such as:

I hope the above reply is helpful to the subject.