A dissolved oxygen and ammonia mass balance for recirculating aquaculture system for the Nile tilapia raising was developed on Python program to achieve two goals. The first goal was to predict the required hourly dissolved oxygen addition and the removal of ammonia from water to attain water quality with optimum range for the Nile tilapia. The second goal focused on designing the required oxygen generator and biofilter. The product of this work is a stand-alone graphical user interface (GUI) program. Users can use it easily in the design and operation of recirculating aquaculture systems. The rates of dissolved oxygen consumption through fish respiration, biological filtration, and the nitrification process were determined in the model structure besides the addition of ammonia through fish. The effect of different growth periods and the average fish mass on dissolved oxygen consumption and ammonia addition were studied. Model validation was conducted. The expected and actual dissolved oxygen consumption by the model were in agreement. In reality, the dissolved oxygen consumption by fish respiration ranged from 1836.76 to 24350.48 mg O₂ h^-1; while in the model, it was from 1830.24 to 23615.26 mg O₂ h^-1. The expected and actual total dissolved oxygen consumption values ranged from 2706.14 to 38950.23 and from 2712.66 to 38697.19 mg O₂ h⁻¹, respectively. The expected average ammonia excretion was from 193.36 to 1699.41 mg h^-1; while theoretically, it was from 194.44 to 1345.50 mg O₂ h^-1. The individual fish weight ranged from 4.26 to 122.79 g in reality. Similarly, it was from 4.22 to 135.86 g during the same period in the results of the model upon validation.