This study was conducted to produce a best method for improving water quality in aquaculture ponds in the acid sulphate soil areas. There are six fish-pond treatments were setup Hoa An Experimental Center - Can Tho University: (I) 100% organic fertilizer (pig manure) use (30 kg/100 m²); (II) biogas slurry use equivalent to 75%TKN in organic fertilizer; (III) biogas slurry use equivalent to 100%TKN in organic fertilizer; (IV) biogas slurry use equivalent to 125%TKN in organic fertilizer; (V) biogas slurry use equivalent to 150%TKN in organic fertilizer; and (VI) fish-pond treatment without using biogas slurry. The results showed that biogas slurry could improve pH of water in acid sulfate soil infected ponds. Indeed, treatment II increased water pH from 3.3 to 6.5 after 1.5 month and maintained at this value until end of the experiment. Dissolved oxygen and Chlorophyll-a were also reasonably high (5.2 ppm and 143.05 µg/L) after 45 days of treatment. Farmers at acid sulphate soil areas could applied this treatment model to improve water quality that serve for aquaculture opportunity, raising income to families.