Koi are usually calm, elegant, and unbothered by the chaos of the world. But every once in a while, one of your fish decides to give you a heart attack by acting weird, floating funny, or gasping like it just ran a marathon. When that happens, you don’t need panic — you need a plan.
This guide walks you through exactly what to do when a koi sends out the aquatic equivalent of a 911 call. Stay calm, think clearly, and remember: koi emergencies are often solvable if you act fast and smart.
1. Don’t Panic — Observe First
Before you rush for nets, medicine, or Google, take a deep breath and look at what’s happening. Many koi behaviors look dramatic but mean very different things.
Observe:
- Is the koi gasping at the surface?
- Is it lying on the bottom?
- Is it swimming sideways, upside down, or erratically?
- Is it isolating from the group?
- Is it flashing (scraping) on the walls or floor?
- Does it have visible wounds or spots?
The goal is simple: before you fix anything, understand what’s wrong. Different emergencies have very different solutions.
2. Test the Water Immediately
Here’s a secret all experienced koi keepers know:
90% of koi emergencies are caused by water quality, not disease.
Your emergency kit should always include a liquid test kit. Check these parameters first — they often explain everything:
- Ammonia: should be 0
- Nitrite: should be 0
- Nitrate: ideally under 40 ppm
- pH: steady, no sudden swings
- KH (alkalinity): enough to stabilize pH
- Temperature: consistent, not rapidly changing
- Oxygen levels: check aeration and water movement
If ammonia or nitrite is above zero: perform an immediate water change and add dechlorinator. This alone can save a koi’s life.
3. Boost Aeration — Right Now
If your koi is breathing heavily, hanging near the surface, or struggling to swim, it may be low on oxygen. Warm weather, algae blooms, medications, and even nighttime plant respiration can drop oxygen dangerously fast.
Increase oxygen immediately by:
- Adding air stones or a larger air pump
- Turning up waterfalls or spillways
- Aiming return jets at the surface for agitation
Even if oxygen isn’t the direct cause, extra aeration helps during almost every emergency.
4. Isolate the Affected Koi (If Necessary)
If one koi is clearly in distress while others appear normal, it may be best to move the sick fish to a quarantine tank.
Good reasons to isolate:
- Severe injuries or ulcers
- Extreme weakness
- Suspected parasite overload (flashing, clamped fins)
- Need for medication that should NOT go into the main pond
But don’t rush to isolate a koi without water testing — if the whole pond has a problem, moving a single fish won’t help.
5. Look for Visible Signs of Illness
Once water quality is checked and aeration boosted, inspect the koi for clues:
- White spots: Ich
- Red streaks in fins: stress, poor water, or infection
- Cotton-like growths: fungus
- Flashing: parasites
- Open sores: ulcers
- Cloudy slime coat: irritation or parasite presence
This helps determine whether further treatment is needed.
6. Never Add Medication Without a Reason
In a koi emergency, the worst instinct is to grab every bottle in your cabinet and “treat just in case.” Don’t do it.
Medication is not a band-aid. In fact, many meds can make sick koi even worse if misused—especially if oxygen is already low.
Only treat when:
- Water quality has been corrected
- You have identified a likely cause
- You’re certain the medication won’t harm the pond or biofilter
- You know the correct dosage
When in doubt: isolate and observe before medicating.
7. Emergency Water Changes — Your Best Friend
If you can’t find the cause right away, a water change is almost always safe and helpful.
A good emergency water change:
- 10–25% of the pond volume
- Dechlorinated (essential!)
- Temperature-matched to avoid shocking the fish
Water changes dilute toxins, stabilize pH, increase oxygen, and reduce stress.
8. Temperature Emergencies: Hot or Cold Shock
If your koi are suddenly distressed, consider temperature:
Heat stress (above 85°F / 29°C):
- Increase shade
- Add aeration
- Avoid feeding
- Add cool water slowly (never dump ice in!)
Cold shock (rapid drops below 55°F / 13°C):
- Stop feeding
- Check heaters or covers
- Allow koi to warm gradually
Koi do not like sudden temperature swings—ever.
9. Emergency Salt Support
Salt can help in many emergencies, especially when koi are stressed or dealing with early irritation.
Safe emergency level: 0.1%–0.15%
This helps with osmoregulation and reduces stress—but only use salt if you know your current salinity level.
Never add salt blindly, and avoid mixing salt with formalin-based treatments.
10. When to Seek Expert Help
Some emergencies truly need a koi-savvy vet or experienced keeper. Get help when:
- The koi has severe buoyancy problems
- Large ulcers or fin rot appear suddenly
- Multiple fish show distress at once
- Your water tests fine but fish still struggle
- The koi becomes unresponsive or cannot swim upright
Quick expert advice can save fish that would otherwise decline rapidly.
Koi emergencies feel scary, but with a clear plan you can take control instead of panicking. Always start with water testing, boost oxygen, observe carefully, and avoid “mystery medication cocktails.” Most emergencies improve dramatically once the root cause is addressed.
Stay calm, act quickly, and let observation and water quality guide your decisions. With the right steps, even a distressed koi can bounce back and return to gliding peacefully through the pond like the living jewels they are.