Soil PH is one of the most important edaphic parameters affecting seed germination of all seed. Quinoa seeds are able to germinate at the poorest conditions. If the soil pH ba variable more than 7.5 and below the 5, Quinoa seed did not good germination.
pH highly influence the germinability of seeds and even if quinoa is indicated as a good germinability rate plant it could not germiante outside the bounds indicated by He Omidi . I would suggest you however to check your temperature and RH% and soil type. Those are all secondary important factors which might decrease your germination rate.
Please check the following articles:
Article Preliminary Research on Seed Production and Nutrient Content...
Quinoa prefers to grow in slightly acidic to alkaline conditions as ideal pH for quinoa ranges from 6 -7.5.
Seed germination is greatly influenced by soil pH. Highly acidic and alkaline condition hampers seed germination due to toxicity of few elements and many other factors.