Koi Quarantine Discharge Criteria: When Is It Safe

By KoiQuanta Editorial Team|Updated Mar 2026

The hardest moment in any quarantine isn't the first 48 hours - it's the decision to end it. I've had fish that looked completely fine for three weeks, passed them to the display pond, and watched an entire collection collapse inside a week. That was before I started using objective discharge criteria instead of gut feeling.

Ending quarantine too early is the most common cause of disease introduction in koi keeping. Full stop. It doesn't matter how good your setup is or how experienced you are - if you're guessing when a fish is ready, you're gambling with everything in that pond.

TL;DR

For standard quarantine from a reputable domestic source, that's 21 days minimum.
For Japanese imports, fish returning from shows, or any fish with unknown health history, 42 days is the floor.
Zero Active Disease Signs for Final 14 Days The last two weeks of quarantine need to be completely clean.
If anything appeared and resolved, the 14-day clock resets from the day of resolution - not from the day you first noticed the problem.
If your quarantine tank runs at 68°F and your display pond is at 74°F, moving a fish directly is a thermal shock.
A fish that's still not feeding 21 days in doesn't pass.
Before transfer, run a 48-hour parameter comparison between the quarantine tank and the display pond.

The Problem With "It Looks Fine"

Appearance is the worst discharge criterion there is. KHV can stay latent for weeks. Bacterial infections can be suppressed by immune response without being resolved. Parasites can drop to undetectable levels and rebound the moment you drop salinity.

The fish that kills your pond will look healthy when you move it. That's the nature of subclinical disease. You need a checklist - not an impression.

The Core Discharge Criteria

1. Minimum Hold Time Met

No exceptions. For standard quarantine from a reputable domestic source, that's 21 days minimum. For Japanese imports, fish returning from shows, or any fish with unknown health history, 42 days is the floor. If KHV is a concern - which it always is with imported fish - the hold time depends on temperature management (more on that below).

If you're cutting the hold short because the fish looks good, you're doing it wrong.

2. Zero Active Disease Signs for Final 14 Days

The last two weeks of quarantine need to be completely clean. No lesions, no behavioral abnormalities, no appetite changes, no respiratory stress, no flashing, no clamped fins. If anything appeared and resolved, the 14-day clock resets from the day of resolution - not from the day you first noticed the problem.

3. All Treatment Courses Completed

Any treatment started during quarantine must be finished. No shortening antibiotic courses because the fish looks better. The minimum antibiotic course runs for the full prescribed duration after you stop seeing symptoms, not when symptoms disappear. I track this in KoiQuanta - the treatment journal flags courses as complete or incomplete.

4. Water Parameters Stable and Within Range

The last 7 days of quarantine should show stable readings across the key parameters:

| Parameter | Target Range |

|-----------|-------------|

| Ammonia | 0 mg/L |

| Nitrite | 0 mg/L |

| pH | 7.2–8.0 |

| KH | 100–150 mg/L |

| Dissolved Oxygen | 7+ mg/L |

| Temperature | Within 1°C of display pond |

That last one - temperature - matters more than people realize. If your quarantine tank runs at 68°F and your display pond is at 74°F, moving a fish directly is a thermal shock. That kind of stress event can trigger a latent infection.

5. Behavior Normal and Consistent

Normal koi behavior in a quarantine tank: active swimming at mid-depth, feeding aggressively when offered food, not hiding, no surface-gasping, no hovering near the return, no isolation from other fish in the tank.

A fish that's still not feeding 21 days in doesn't pass. Something is suppressing that appetite - and that something is going to your pond.

6. Water Parameters Matched to Display Pond

This is often skipped. Before transfer, run a 48-hour parameter comparison between the quarantine tank and the display pond. Match:

Temperature (within 1°C)
pH (within 0.3 units)
Salinity (if you've been running salt, gradual reduction prior to transfer)

If salt treatment was part of your protocol, taper it down 5–7 days before discharge. You don't want to move a fish from 0.3% salt into a salt-free pond - the osmotic shift adds unnecessary stress.

KHV-Specific Discharge Criteria

KHV is the reason 21-day quarantine has limits. The virus needs specific temperature windows to express - roughly 63–77°F (17–25°C). If fish were quarantined below this range the whole time, you can't rule it out.

For Japanese imports or any fish with KHV exposure risk, proper discharge requires:

Minimum 30 days at temperatures within the KHV-active range (65–75°F)
Observation during the full temperature window with no clinical signs
Ideally, KHV PCR testing ($35–50/fish) before discharge

No PCR test is required for domestic fish from a trusted source with clean history. For a $3,000 Kohaku nisai from Sakai, the test cost is trivial.

Post-Treatment Hold Time

If you treated for anything - bacterial, parasitic, viral - there's a mandatory observation hold after the last treatment dose:

Salt treatment: 5–7 days post-treatment before discharge
Antibiotic course: 7–14 days post-final dose with no relapse
Praziquantel: 7 days post-treatment with scrape confirmation negative
Potassium permanganate: 5 days post-final dip with full behavioral recovery

The issue isn't drug residue. It's confirming the disease didn't come back. Parasites in particular can resurge after treatment ends if the lifecycle wasn't fully interrupted.

The Discharge Checklist

I run this before any pond transfer. KoiQuanta generates it automatically, but here's the logic:

[ ] Minimum hold time reached (21 days domestic / 42 days import / PCR-cleared KHV risk)
[ ] 14 consecutive days of zero disease signs in the final observation window
[ ] All treatment courses documented as complete in the treatment journal
[ ] Ammonia: 0, Nitrite: 0 for 7 days straight
[ ] pH, KH, temperature stable and documented
[ ] Fish feeding normally and behaving normally for final 7 days
[ ] Temperature matched within 1°C of display pond
[ ] Salt tapered if used (3–5 days of gradual reduction complete)
[ ] No new fish added to quarantine tank in the final 14 days
[ ] Photo documentation current and shows no active lesions

If any item isn't checked, the fish doesn't move. Period.

Common Mistakes at Discharge

Moving fish based on calendar, not criteria. "It's been 30 days" is not a discharge criterion. 30 days with 14 clean observation days and completed parameters is.

Skipping temperature matching. The stress of a 5°F temperature swing can trigger latent infections in fish that were genuinely clear.

Not completing salt taper. Moving directly from 0.3% salt to 0% is an osmotic event. It stresses fish unnecessarily.

Not confirming appetite. A fish that stopped eating on day 18 and "seems fine" on day 21 hasn't had enough time in normal feeding behavior to confirm recovery.

Discharging multiple fish from a batch when only some are ready. If one fish in a batch fails criteria, the whole batch stays. Cross-contamination within the tank means you can't declare individuals clear independently.

FAQ

What criteria must a koi meet to pass quarantine?

A koi must complete the full minimum hold time, show no disease signs for the final 14 consecutive days, have all treatment courses documented as complete, display stable water parameters including zero ammonia and nitrite, and demonstrate normal feeding and behavior throughout the final observation window.

How long after treatment can I discharge a koi?

The post-treatment hold varies by treatment type: 7–14 days after antibiotics, 7 days after praziquantel with a negative scrape, and 5–7 days after salt treatment. The clock starts from the last dose, not from symptom disappearance. Any relapse of symptoms resets the hold entirely.

What water parameters must match before transferring koi?

Temperature is the most critical - within 1°C of the display pond. pH should be within 0.3 units. Ammonia and nitrite must be zero. If salt was used in quarantine, it should be fully tapered before transfer. Running a 48-hour parameter comparison between the two systems before any transfer is standard practice.

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Sources

Associated Koi Clubs of America (AKCA)
Koi Organisation International (KOI)
University of Florida IFAS Extension Aquaculture Program
Fish Vet Group
Water Quality Association