Use the table below to select the correctly sized item. If you have any difficulties deciding which size is right for you, contact us by email or phone and we will be very happy to assist you. Although many factors including humidity, temperature, stocking density and surface area to pond volume ratio, can affect the Oxygen levels within a pond. We generally recommend a minimum air flowrate of: 100 Litres Per Hour (1.7 Litres Per Minute) / 1000 Litres (220 Gallons) of Pond Volume Or 450 Litres Per Hour (7.5 Litres Per minute) / 1000 Gallons (4500 Litres) of Pond Volume Air Pump | Litre Per Min | Litre Per Hour | Wattage | Max Air Stones | Max Pumping Depth | Approx. Optimum Pumping Depth | Hozelock Air 320 - 5 LPM | 5 | 320 | 4w | 2 | 1.2m | 0.6m | Hozelock Air 640 - 10 LPM | 10 | 640 | 8w | 4 | 1.2m | 0.6m | Hozelock Air 1500 - 25 LPM | 25 | 1500 | 17w | 6 | 2m | 1m | Hozelock Air 2700 - 45 LPM | 45 | 2700 | 35w | 12 | 2m | 1m | Hozelock Air 4500 - 75 LPM | 75 | 4500 | 35w | 12 | 3m | 1.5m | |