A 90- day outdoor trial was conducted in cemented tanks (2.4 m3) with 10 cm soil base to evaluate the performance of different carbohydrate supplementation on water quality and growth performance of common carp fingerlings under mid-hill altitude. Six carbohydrate sources viz. ricepolish (T₁), wheat flour (T₂), sweet potato (T₃), yam (T₄), tapioca (T₅), and rice husk (T₆) were used to maintain the optimum C:N ratio of 10:1 to produce biofloc within the culture system. Common carp fingerlings (9.1±0.2 gm) were stocked @ 10 nos. /m3 and fed with formulated feed (20% CP) @ 4% body weight daily. During the experiment there was no aeration provided and water also not exchanged throughout the trial period. A control (C) was maintained without addition of carbohydrate source. The study indicated a significant reduction (p<0.05) in total ammonia nitrogen (TAN) load in water for the all treatments (T1 to T5) compared to control. There was a significant difference in water quality parameters viz. pH, dissolved oxygen, free carbon-di-oxide (CO₂), alkalinity, and hardness among the treatment groups. The total dissolved solids (TDS), and conductivity were not differed significantly between the treatments. Further, significantly lowered (p<0.05) feed conversion ratio (AFCR) was found for T₃ to T₅ than T₂, T₆ and control. The maximum growth increment in terms of biomass was observed in T₃ @ 32.12% than T₁ @ 21.45% compared to control. The present study indicates that the addition of tuber crops, rice polish as carbohydrate source with low protein diet at a specific ratio can improves water quality and enhances the growth of common carp.