You can buy vegetable broth powder at Asian grocery stores and health stores. Depending on the strength of the broth, feel free to add more if preferred.
Quinoa needs to be thoroughly rinsed with water before use. Otherwise, it will taste bitter. I usually rinse it by putting quinoa in a mesh strainer and running water through it.
Quinoa absorbs more liquid overtime. If soup becomes too thick, simply add more water and vegetable broth.