How to use this calculator
- Enter or choose fish biomass.
- Enter or choose oxygen consumption rate.
- Enter or choose dissolved oxygen of inflow water.
- Enter or choose minimum dissolved oxygen to keep.
- Enter or choose oxygen added per aerator (field rate).
- The oxygen demand updates as you type. Use Copy result or Share to keep it.
Method
Demand (mg/h) = Biomass × Rate; Flow (L/h) = Demand ÷ (DO_in − DO_min); Aerators = ⌈Demand (kg/h) ÷ Aerator rate⌉
- Rate
- mg of oxygen used per kg of fish per hour
- DO_in
- oxygen in the incoming water, mg/L
- DO_min
- lowest oxygen level you will allow in the tank or pond
Worked example
- Demand = 2,000 kg × 300 mg/kg/h = 600,000 mg/h = 600 g/h, or 14.4 kg a day.
- Each litre of inflow can give up 8 − 5 = 3 mg, so flow = 600,000 ÷ 3 = 200,000 L/h = 200 m³/h.
- Aerators: 0.6 kg/h ÷ 0.5 kg/h = 1.2, so 2 aerators.
Two tonnes of fish using 300 mg/kg/h need 14.4 kg of oxygen a day: 200 m³/h of water flow or two 0.5 kg/h aerators.
What the result means
Oxygen use peaks after feeding and at high temperature, and ponds lose oxygen to algae and sediment at night. Size aeration for the worst hours, not the daily average.
Assumptions and limits
- Consumption rate is constant over the period.
- The fish are the only oxygen consumer.
- Pond respiration by plankton and sediment, and oxygen added by photosynthesis, are not included.
Questions
Where do I get the oxygen consumption rate?
From research or extension data for your species at your water temperature and fish size, or from your equipment supplier. Small fish use more oxygen per kg than large fish.
Why is the aerator rating reduced?
Makers rate aerators in clean water with zero oxygen. In a stocked pond, transfer is lower, so use a field figure rather than the standard rating.