The most harmful nitrogenous compounds in fish-breeding place using are ammonia and nitrate. Excessively high total nitrogen concentration is the signal of unbalance for breeding fishes in seawater and may result overfeeding or overstocking without seawater treatment system. The failure of elimination for the organic ingredients or nitrogen compounds can also cause the consequence of inadequate oxygen concentration in seawater, either. The study shows the effect of biofilter and W disinfector of seawater in the fish- breeding place. In the results, these tools had ammonia, nitrite, nitrate and decreased 71.8%, 27.6% and 1%, respectively, and the total number of microorganisms decreased up to 81.9%.