Wastewater streams are a low-cost nutrient source for cultivating microalgae and cyanobacteria. However, single streams often exhibit imbalanced nutrient profiles, insufficient to support optimal microbial growth. Mixing streams with complementary physicochemical properties can balance nutrients and eliminate the need for external supplementation. Optimizing the mixing ratio is essential to achieve favorable carbon-to-nitrogen (C:N) ratios, enhance biomass and biocompound production, and improve culture conditions such as turbidity and pH. This study aimed to identify the optimal mixing ratio of two agro-industrial wastewaters, second cheese whey (SCW) and poultry wastewater (PW), for the cultivation of a Leptolyngbya-dominated consortium. SCW had higher organic and lower inorganic nutrient content than PW. Increasing the SCW proportion raised the C:N ratio and induced N and P limitations, conditions known to promote lipid accumulation. Four SCW:PW ratios (50:50%, 60:40%, 70:30% and 85:15%) were examined based on the initial dissolved chemical oxygen demand (d-COD) concentration of 3000 mg L⁻¹. The 60:40% and 70:30% SCW:PW ratios yielded the highest biomass productivities (276.6 and 268.3 mg L⁻¹ d^−1, respectively), while the 50:50% resulted in the lowest productivity (174.6 mg L⁻¹ d⁻¹), likely due to turbidity. A progressive enhancement in pollutant removal efficiency was observed with increasing SCW proportions. The 70:30% ratio achieved the highest d-COD (89.2%), total nitrogen (64%) and PO₄^3--P (60%) removal, as well as the highest lipid content (14.0% d.w.). This ratio was identified as optimal. The 85:15% ratio also demonstrated enhanced lipid content (11.9% d.w.), attributed to the reduced turbidity and consequent improved light penetration, favoring the proliferation of lipid-producing autotrophic microorganisms within the consortium.