This study aimed to evaluate the hemato-biochemical parameters, oxidative stress indices and histopathological alterations in different organs after exposure of fish to calcium hypochlorite (Ca(OCl)2) as well as granular activated carbon (GAC) (unrinsed) as dechlorinator. A total of 96 Clarias gariepinus was divided equally into four groups in triplicates: Group 1 was kept as a control, while groups 2, 3, and 4 were exposed (daily) to Ca(OCl)2 at a concentration of 0.045mg/L water, GAC at a concentration of 50mg/L water and Ca(OCl)2 plus GAC at a same concentration of previous groups, respectively. The exposures were conducted for 96h after that blood and tissue samples were collected for performing experimental tests. The results revealed that significant increase in erythrogram and leukogram parameters, besides increase activities of serum alanine aminotransferase and aspartate aminotransferase and concentrations of bilirubin fractions, total proteins, globulins, sodium, chloride, calcium, phosphorus and ammonia in all experimental groups. Fourth group showed insignificant increase in red blood cells and monocytes counts. Hyperalbuminemia was observed in Ca(OCl)2 group alone. Serum alkaline phosphatase activity and creatinine concentration were significantly decreased in all experimental groups. Malondialdehyde and hydrogen peroxide levels showed significant increase, besides superoxide dismutase activity was decreased significantly in all experimental groups in the liver, kidneys and gills tissues. In conclusion, chlorine caused hematological disturbances, hepato-renal impairment with oxidative stress. Despite the importance of GAC as dechlorinator, it caused several adverse results under the condition of this experiment, and this sheds light into the importance of safely use of GAC on aquatic organisms.