You’ve just received a beautiful new koi — maybe a stunning Kohaku or a shimmering Yamabuki Ogon. The temptation to drop it straight into your pond is real. But if you have existing fish, skipping quarantine is one of the riskiest things you can do as a koi keeper.
At Crystal Creek Koi Farm, we raise every fish in carefully monitored conditions. But even so, we strongly recommend quarantine for every new koi — regardless of source. Here’s why, and exactly how to do it.
Why Quarantine Is Non-Negotiable
A koi can look perfectly healthy and still carry parasites, bacteria, or viruses that are invisible to the naked eye. Common threats include:
- Koi Herpesvirus (KHV) — a highly contagious and often fatal virus with no cure
- Ich (white spot disease) — caused by a parasite that spreads rapidly in pond conditions
- Flukes — microscopic gill and skin parasites that cause serious irritation and immune stress
- Aeromonas & Pseudomonas — bacterial infections that cause ulcers, fin rot, and systemic illness
A single infected fish introduced directly into your pond can wipe out your entire collection within days. Quarantine creates a critical buffer that protects every fish you’ve already invested in.
Setting Up Your Quarantine Tank
You don’t need an elaborate setup — but it does need to be functional and completely separate from your main pond.
Tank Size
Use a bare-bottom tank or stock tank of at least 100–300 gallons for most koi. Bare-bottom is preferred — it’s easier to clean and monitor waste. Skip the gravel and decorations, which can harbor bacteria and make disinfection difficult.
Filtration
A sponge filter or canister filter works well. If possible, seed it with media or water from your established pond filter to introduce beneficial bacteria and jump-start the nitrogen cycle. Without an established cycle, ammonia can spike quickly — test daily and do partial water changes as needed.
Aeration
Run an air stone connected to an air pump at all times. Stressed fish have higher oxygen demands, and some medications reduce dissolved oxygen. Keep aeration strong throughout the quarantine period.
Temperature
Use a submersible heater to keep the quarantine tank within 2°F of your pond temperature. Temperature swings suppress the immune system. Always use a thermometer to monitor both environments before transferring fish.
Dedicated Equipment
This is critical: never share nets, buckets, or siphons between your quarantine tank and main pond. Keep a completely separate set of tools for the quarantine tank. If equipment must be shared, disinfect with a diluted bleach solution (1:9 bleach to water) and rinse thoroughly before use.
Placing Your New Koi in Quarantine
Once your quarantine tank is set up and running, follow these steps:
- Acclimate first — Float the sealed bag in the quarantine tank for 15–20 minutes to equalize temperature. Then slowly add quarantine tank water to the bag every 5–10 minutes over 30–45 minutes. See our full acclimation guide for details.
- Transfer the fish, not the water — Use a soft net or wet hands to move the koi into the quarantine tank. Discard the bag water — do not add it to your tank.
- Optional salt treatment — Many keepers add non-iodized salt at 0.3% salinity (about 2.5 lbs per 100 gallons) to reduce osmotic stress and deter external parasites. Do not use iodized salt or salt with additives.
- Observe daily — Watch closely for signs of illness over the next 2–4 weeks.
What to Watch For During Quarantine
Check your fish every day. Signs that something may be wrong include:
- Clamped fins held tight against the body
- Flashing — rubbing or scratching against tank surfaces
- White spots, patches, or excess mucus on the body
- Ulcers, sores, or red streaking on the skin
- Labored or rapid gill movement
- Lethargy, loss of appetite, or erratic swimming
If you notice any of these symptoms, consult a koi health professional before introducing the fish to your main pond — and before treating, as different conditions require different approaches.
How Long Should Quarantine Last?
A minimum of 2 weeks is recommended, but 4 weeks is the gold standard. Many diseases — including KHV — have incubation periods that won’t show symptoms until well into the second or third week. The longer you observe, the more confident you can be that your new fish is healthy.
Introducing to the Main Pond
After a clean quarantine period with no signs of illness and stable water parameters, your new koi is ready for the main pond. Acclimate it to the pond water using the same slow drip method before releasing it. Observe your existing fish closely for the first week after introduction as an added precaution.
Questions? We’re Here to Help
Quarantine can feel like extra work, but it’s the single most effective thing you can do to protect your pond. If you have questions about setting up a quarantine tank or your new fish’s health, contact us — we’re always happy to help.
For more detail, visit our full Importance of Quarantine guide.
Happy and healthy ponding! 🐟