As the demand for transmission capacity and traffic increases, according to Cisco's Global Internet user growth statistics, the task of reliable data transmission remains relevant. Forward error correction (FEC) codes are now one of the most critical essential methods in wavelength division multiplexing (WDM) transmission systems to increase data transmission's reliability and improve the quality of transmission (QoT). The main limitation of transmission systems is the high bit transmission rate without errors. If these errors are not found and corrected, data loss may be possible. For effective communication, data must be transmitted with high accuracy. This can be achieved by first identifying errors and then correcting them. This paper compares codes suitable for detecting and correcting errors, such as Reed–Solomon (RS). The RS codes are nonbinary Bose-Chaudhuri-Hocquenghem (BCH) codes with code symbols from Galois fields are essential error-correcting codes. The advantage of using such codes is that the system can achieve the lowest bit error ratio (BER) with a lower transmitter output power. In this paper, we investigate the performance of 8 and 16-channel wavelength division multiplexed passive optical network (WDM-PON) by implementing FEC codes such as Reed-Solomon (RS), 6.7%, and 8.5% overhead (OH), used for long-distance optical transmission in telecommunication systems as defined in ITU-T G.709 and ITU-T G.975 standardizations. For additional performance, the authors suggest using different channel spacing of 50 GHz and 100 GHz. This paper compares the performance of 8 and 16-channel 100 GHz spaced WDM-PON transmission systems with the data rate of 10 Gbit/s per lambda using ITU-T G.652 recommendation compliant optical fiber - standard single-mode fiber (SSMF).