Water Quality, Pond Management and Fish Health
Water Quality, Pond Management and Fish Health
This domain tests pond water and soil management and the recognition of fish disease. Many marks come from linking a parameter to a management action.
Core rules
- Dissolved oxygen should stay above 5 mg/L; low DO at dawn causes gasping and mortality.
- pH 6.5–8.5 is suitable. Liming raises pH and alkalinity but must not be applied together with fertiliser.
- Unionised ammonia is toxic; it rises with high pH and temperature. Test total ammonia and interpret with pH.
- Transparency of 30–40 cm indicates healthy plankton; too clear water means poor fertility, too green means bloom risk.
- Biosecurity: quarantine new stock, disinfect nets, avoid overcrowding, and remove dead fish promptly.
Worked example
A pond is 1,000 m² with an average depth of 1.5 m. Volume = 1,000 × 1.5 = 1,500 m³. To apply a dose of 1 ppm (1 g/m³) of a treatment, mass = 1,500 × 1 = 1,500 g = 1.5 kg. If the label says 2 ppm, use 3 kg. Weigh the chemical; do not estimate by scoop.
Traps
Do not apply lime and manure on the same day; do not treat with antibiotics without diagnosis; do not assume clear water is healthy; and do not confuse total ammonia with the toxic unionised fraction.