This study was carried out to investigate the effect of a magnetic field on some physicochemical water parameters including (temperature, pH, dissolved oxygen, nitrogenous substances with organic matter, salinity, electrical conductivity, chloride, total hardness, calcium (Ca²), and magnesium (Mg⁺²), lead and iron) ; as well as performance and some mineral contents of Oreochromis niloticus. 240 out of 300 apparent healthy Oreochromis niloticus (21.4 ± 0.39 g) were randomly cultured for 60 days in either control or magnetized water at power of 21.57 Milli Tesla (triplicate tank per treatment). Magnetically treated water had a significantly higher pH; electrical conductivity (EC) and salinity, while iron was significantly (p≤0.01) lower; nevertheless, other studied water parameters showed non-significant changes. Fish in magnetically treated water showed an improvement in growth performance measures that were significant (p≤0.01) in weight (g) and length (cm), with weight gain trending upward at the 30^th and 60^th days. Furthermore, fish mineral levels were improved in the magnetically treated water group as compared to the control group. Our analysis revealed that using a magnetic field with a strength of 21.57 mT in a one cubic meter fish tank for three hours and then resting for one hour improved both water quality parameters and fish performance, and that the magnetic field exposure kept water quality parameters as close or even better than the control group, despite the fact that the minimum water exchange in magnetized water tanks was applied.