Asian Journal of Environment & Ecology

Water quality is a central determinant of productivity and fish health in pond aquaculture, yet single-time observations may not capture within-day variation. This study evaluated diurnal changes in selected physicochemical parameters in a semi-intensive composite carp culture pond at Sawaikachhar village, Kabirdham district, Chhattisgarh, India, during November–December 2021. The pond was fertilised periodically with cow dung and urea and was managed without supplementary feeding. Water samples were collected weekly for six consecutive weeks at 06:30 h, 12:00 h, and 16:30 h. The parameters assessed were water temperature, dissolved oxygen, pH, free carbon dioxide, total alkalinity, total hardness, and transparency. Temperature ranged from 22 to 27°C and generally increased from morning to midday. Dissolved oxygen ranged from 3.57 to 6.87 mg L⁻¹, with the lowest values occurring in the morning and higher values recorded later in the day. The pH remained slightly alkaline, ranging from 7.53 to 8.23, while free carbon dioxide ranged from 5.00 to 11.30 mg L⁻¹ and declined from morning to evening. Alkalinity, hardness, and transparency remained within ranges generally suitable for carp culture. The results indicate that photosynthesis, respiration, and buffering processes shaped daily pond-water chemistry, supporting the need for early-morning and routine monitoring in semi-intensive carp ponds.