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Pond fish stocking calculator
A guideline for how many goldfish or koi a pond can carry once they are adult size. Stocking is a starting point — filtration, plants and feeding matter just as much.
The rules behind it
- Goldfish, shubunkins, orfe: 1 inch of adult fish per 10 US gallons with good filtration, 1 inch per 20 gallons without. Adult pond goldfish reach about 6 in, so that is one fish per 60–120 gallons.
- Koi: grow to 18–24 in and produce far more waste. Plan at least 1,000 US gallons (3,800 L) for the first koi and about 250 gallons per koi overall.
- Depth: at least 2 ft (60 cm) for goldfish and 3 ft (90 cm) for koi, so there is cool water in summer and unfrozen water in winter.
Fish grow into the space. A pond that looks empty with ten 2-inch goldfish will be crowded in three summers — and goldfish breed. Stock a few at a time and watch the water: green water, foam and fish gasping at the surface at dawn are signs of overstocking.
Questions
How many goldfish can I put in a 500-gallon pond?
About 4–8 adult goldfish: 500 ÷ 120 = 4 without a filter, 500 ÷ 60 = 8 with a filter sized for the pond.
How many koi can I keep in a 1,000-gallon pond?
Up to about 4 by the 250-gallons-per-koi rule. Many serious koi keepers give each adult 500–1,000 gallons.