Quarantine keeps newly purchased koi in a separate system while you observe their health and manage transport stress. It reduces the chance of exposing the whole pond to an undetected problem. It does not certify that a fish is free of every pathogen.
Build the System Before Buying Fish
Choose a smooth, fish-safe tank with room for the number and size of koi being held. Its actual water volume matters for filtration and any prescribed treatment. A small tub with an air stone alone is not a complete long-term quarantine system.
- Working biological filtration with adequate circulation and aeration.
- A secure cover that prevents jumping without preventing gas exchange.
- A thermometer and test kits for ammonia, nitrite, pH, and alkalinity.
- Dedicated nets, bowls, hoses, and other equipment.
- A way to make controlled, treated water changes and safely remove waste.
Keep the system physically separate from the main pond. Avoid shared water, splashes, and wet equipment. Care for established fish before quarantine fish, and clean hands and equipment appropriately between systems.
How Long Should Quarantine Last?
Aquatic Veterinary Services recommends a 4–6 week quarantine, with duration influenced by conditions. University of Florida guidance for KHV specifies at least 30 days under its defined temperature protocol. These are condition-dependent protocols, not a countdown that makes a fish safe automatically. Plan the protocol with the supplier and, where appropriate, a fish veterinarian.
If illness appears or treatment is needed, reassess the release date with your veterinarian. Cold conditions can delay signs of some infections. Do not heat fish abruptly or attempt a disease challenge on your own.
Keep a Daily Record
- Temperature and water-test results, including ammonia and nitrite.
- Breathing, swimming, appetite when feeding is appropriate, skin, and fins.
- Water changes, feeding amounts, equipment problems, and any treatment.
Do not add salt, parasite medications, or antibiotics automatically. Treatment should address an identified problem and use the measured system volume. Equating one pound per 100 US gallons with 1% salt was incorrect: that amount is approximately 0.12% weight/volume. This arithmetic correction is not a treatment recommendation.
What Quarantine Cannot Prove
A koi that looks healthy after warm quarantine is not necessarily KHV-free. University of Florida notes that negative tests cannot exclude every carrier. A veterinarian can explain testing options and limitations. Do not use an apparently healthy resident fish as a casual test companion.
Before Release
Resolve unexplained signs, confirm stable water and normal behavior, complete the agreed observation or treatment plan, and compare the pond with quarantine water before transfer. Keep the records; they are useful if a later concern arises.
Sources: Aquatic Veterinary Services: Quarantine Your Fish Yourself; UF/IFAS: Koi Herpesvirus Disease. For abnormal behavior, start with the health guide.