The research aims to evaluate the impact of stocking density, ranging from 5 to 25 fry per aquarium, on the water quality for red tilapia (
Oreochromis niloticus) in freshwater aquariums, particularly when zeolite is added. Furthermore, the study intends to compare the water quality of fish in treatments with and without zeolite across various stocking densities. Zeolite was added in order to lessen the impact of polluted water quality. Red tilapia fry (12.90±0.01 g, 81.95±0.02 cm) were stocked into each aquarium (40×20×20 cm). Five treatments (containing zeolite and without zeolite) with replicates: 5, 10, 15, 20, and 25 fry/aquarium were prepared. Fish were fed twice a day with 2% of total biomass of each fish. The water quality parameters of each aquarium were monitored by using YSI model 556 multi-parameter and UV-VIS spectrophotometer. Based on the water quality recorded, significant differences (p<0.5) were found in all water quality parameters among treatments except salinity. The water quality recorded in zeolite supplemented treatments was better than in control. Practitioners can benefit from the results of this study as they seek to grasp the optimal stocking density in a closed system supplemented with zeolite.