Surface area tools
Aeration sizing
Air delivery estimate
Not calculatedCFM
De-icer wattage
De-icer estimate
Not calculatedW
Gas-exchange stocking limit
Total fish length limit
Not calculatedin
These are rules of thumb. Filtration, fish load, weather and existing circulation affect actual needs. Check equipment ratings and water quality before using these estimates.
Surface area methods
CFM = surface area (sq ft) ÷ K
K = 750 cool · 500 warm · 300 hot
watts = surface area (sq ft) × W, rounded up to the next common de-icer size
W = 7 mild · 10 cold · 15 severe
max inches = surface area (sq ft) ÷ D
D = 1 goldfish-type · 3 koi
Aeration assumes a still ornamental pond with moderate stocking and a minimum 1 CFM pump. Heavy stocking or algae can increase demand.
De-icer sizing assumes a sheltered site and an opening for gas exchange. It does not size a heater for the whole pond; wind may require more wattage. Follow the manufacturer’s rating.
The stocking estimate covers gas exchange only. It excludes filtration, feeding and bacterial capacity. Stay below the estimate and test water quality.