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"Juveniles of P. indicus weighing 0.60 � 0.07g (5.0 � 0.7cm) were reared in brackishwater containing various ammonia concentrations ranging from 1 to 2mg NH3 -N/l for the treatment of zeolite I and II, formalin and BN10 for knowing the efficiency of ammonia removal in shrimp rearing system. Observation showed that at higher concentrations of ammonia in the media, zeolite I and II could remove 30 �g NH3-N/l in 24 h duration. Bioassay study affirmed that the LC0, LC50 and LC100 values for P. indicus experimented in formalin varying from 30 to 80 mg/l were 30, 60 and 80 mg/l respectively. The SAR calculated for P. indicus was found to be 22.5 mg/l. The rate of ammonia removal by formalin was varying from 88 to 111% in the aerated medium and 70 to 87% in the non-aerated medium. The ammonia removal efficiency of formalin was lowered (17 - 52%) due to excretion by the shrimp. Formalin chemical was observed to significantly reduce the phytoplankton productivity. A lowest value of 5 mg C/m3/h production was noticed in shrimp rearing system treated with the highest concentration of formalin (20 mg/l). 5 to 25 mg/l of formalin concentration required KMnO4 concentration varying between 8.2 and 30.0 mg/l for oxidation purpose. The O : N ratio was found to decline from 16:1 to 3:1 in media treated with 1 and 2mg NH3 -N/l. Lyophilised nitrifying bacteria (BN10) accelerated nitrification process within 21 days. The recommended level of formalin for shrimp rearing system was found to be 10 mg/l for ammonia concentration up to 2mg N/l. The influence of the organic acid (formalin) and ion exchanger (zeolites) experimented for the removal of ammonia and the important outcome of the investigation are discussed in details for safe application and dissemination of these information to shrimp farmers for field application."