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Adding Goldfish to a Large Koi Pond: Compatibility and Filtration

5,000-gal koi pond with six 12"+ koi. Asks about adding four 4" goldfish and running waterfall filter continuously.

Compatibility

Koi and goldfish coexist well. Risks: new fish may introduce parasites (quarantine recommended). Goldfish breed prolifically—may outnumber koi fry. Predators often control population.

Filtration

Run waterfall filter 24/7 for biological filtration and aeration. Oxygen critical for koi. In winter, if waterfall off, add air stone. Pumps/filters should run continuously.

Pond and Water Gardening: Fish Lying on Side at Pond Bottom: What to Do; Ghost Koi & Goldfish Compatibility: Behavior, Stocking & Predator Awareness; Fish Hiding After Predator Visit: Recovery Timeline & Protection; Building a Koi Pond: Depth Requirements and Planting Water Lilies; Moving Indoor Goldfish to an Outdoor Pond for Winter; Black Water in a New 4,000-Gallon Koi Pond: Causes & Concerns; Adding a Second Koi to a 2,000+ Gallon Pond with Goldfish; Ulcers on Goldfish and Koi: Aeromonas Infection and Treatment; Sexing Koi and Clearing Green Water; Koi Dying, Goldfish Fine: Red Worms in Filter, New Pond Syndrome

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