Fish Diseases and Management

6.3.1.6 Too low (acidic) pH

Fishes differ in their optimal pH range. A pH range of 6.5 to 9.0 is generally recommended for freshwater fish. Values outside this range are stressful. A pH of < 4.0 or > 11.0 is lethal. As a treatment if the pond alkalinity is less than 50 mg/l as CaCO_3, buffer should be added. Addition of agricultural lime, slaked lime, sodium hydroxide increases the alkalinity.