D. SanjayasariN. Andriyani2016-03-222016-03-222016-03-22978-979-792-437-9wahyu sari yenihttp://repository.unri.ac.id/xmlui/handle/123456789/8101The study was to determine the effectiveness of two different activated carbons in reducing total hardnessas one of principal component in water quality and also their affect to oxygen consumption rate in Nile Tilapia. The present of Ca and Mg in water has become essential as micronutrient for aquaculture. Unfortunately it became a threat when the level was above average.Aactivated carbon from agriculture waste became one of solution to solve high hardness in the water. The treatments were P0 (control with no carbon active), P1 (coconut shell) and P2 (rice husk). The research was used Completely Randomized Design (CRD) with five replications. The result showed water quality parameters still in range with pH 6-8 and temperature of 280C. Meanwhile, the best result of total hardness reduction was expressed significantly (P<0,01) 78,9% by P2 rise husk activated carbon. The same result was expressed by P2 treatments (P<0,01) in oxygen consumption rate of Nile Tilapia. Based on the research concluded that rise husk activated carbon gave the best performance in reducing water hardness and increasing oxygen consumption efficiency of Nile Tilapia.enactivated carbonhardnessoxygen consumptionNile TilapiaUR-Proceedings