Koi Quarantine Salt Treatment: Concentrations, Dosing, and Limits

By KoiQuanta Editorial Team|Updated Mar 2026

Salt is the most-used treatment in koi quarantine - and the most misused. Too little does nothing. Too much stresses the fish. Added all at once rather than gradually, it can cause osmotic shock. And salt alone won't resolve a fluke infestation, a KHV infection, or a bacterial ulcer.

Know what salt does, how to dose it correctly, and when you need something more.

TL;DR

Adding salt to 0.1-0.3% reduces the osmotic gradient, making it easier for stressed fish to maintain internal balance.
Here's why: it's 3 grams/liter, and there are 3.785 liters per gallon, so 3 × 3.785 = ~11.35 grams per gallon.
100 gallons × 11.35 g = 1,135 grams = 2.5 lbs.
Fill a 5-gallon bucket with tank water 2.
Add salt to the bucket and stir until dissolved 3.
Pour bucket contents into the tank over a high-flow area 4.
If you change 20% of the water (e.g., 60 gallons in a 300-gallon tank), you need to add 20% of your total salt dose back to maintain concentration.

What Salt Actually Does

Salt (sodium chloride, NaCl) works in koi quarantine through two mechanisms:

Osmotic protection. Fish are hyperosmotic to fresh water - they're constantly losing salt to the surrounding water and working to maintain internal salt balance. Sick or stressed fish have compromised osmoregulatory function. Adding salt to 0.1-0.3% reduces the osmotic gradient, making it easier for stressed fish to maintain internal balance. This is supportive, not curative.

Antiparasitic action. At 0.3-0.5%, salt disrupts the osmoregulation of many external parasites, particularly:

Trichodina and other ciliated protozoa
Costia (Ichthyobodo necatrix)
Some reduction in white spot (ich) when combined with heat

Salt does NOT effectively kill:

Monogenean flukes (Gyrodactylus, Dactylogyrus) - these need praziquantel
Ich in the encysted and reproductive stages - need heat treatment or specific medications
Crustacean parasites (anchor worm, lice)
Any bacterial, fungal, or viral pathogens
KHV - there is no salt treatment for KHV

Salt Concentrations and What They're Used For

| Concentration | Dose per 100 gallons | Use |

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

| 0.1% | 0.83 lbs | Minimal osmotic support, very stressed fish |

| 0.2% | 1.67 lbs | Mild osmotic support, acclimation |

| 0.3% | 2.5 lbs | Standard prophylactic quarantine |

| 0.5% | 4.2 lbs | Active parasite treatment, post-show quarantine |

| 0.6-0.9% | 5-7.5 lbs | Brief dip treatment (minutes only), not extended bath |

| 3% | 25 lbs | Short dip (3-5 minutes) for severe external infections |

Standard quarantine protocol: build to 0.3% over 48 hours and maintain for the quarantine duration.

Active parasite concern: build to 0.5% over 72 hours.

Do not maintain above 0.5% for extended periods. Prolonged exposure to 0.6%+ is stressful for koi, particularly smaller fish and tosai.

Dosing Math

The calculation everyone gets wrong: you're making a weight-to-volume percentage, not a volume-to-volume percentage.

0.3% salt solution:

3 grams of salt per liter of water
Or 1.26 lbs of salt per 100 gallons of water (commonly rounded to 1.25 lbs)
Or about 2.5 lbs per 100 gallons if you're building from 0% to 0.3% in a single step

Wait - those numbers seem contradictory. Here's why: it's 3 grams/liter, and there are 3.785 liters per gallon, so 3 × 3.785 = ~11.35 grams per gallon. 100 gallons × 11.35 g = 1,135 grams = 2.5 lbs.

Quick reference:

To reach 0.3% in a tank starting at 0% salinity:

100 gallons: 2.5 lbs of salt
200 gallons: 5 lbs
300 gallons: 7.5 lbs
500 gallons: 12.5 lbs
1,000 gallons: 25 lbs

To reach 0.5%:

100 gallons: 4.2 lbs
300 gallons: 12.5 lbs
500 gallons: 21 lbs

How to Add Salt Correctly

Never dump the full dose in at once. Rapid osmotic changes stress fish even when the target concentration is appropriate.

Method 1 (recommended): Dissolved in bucket

Fill a 5-gallon bucket with tank water
Add salt to the bucket and stir until dissolved
Pour bucket contents into the tank over a high-flow area
Repeat until full dose is added over 24-48 hours

Gradual build schedule for 0.3% target:

Day 1: Add 1/3 of total dose (reach 0.1%)
Day 2: Add 1/3 of total dose (reach 0.2%)
Day 3: Add remaining 1/3 (reach 0.3%)

For 0.5% target:

Same gradual approach, building over 3-4 days

Water Changes and Salt Management

When you do water changes during a salted quarantine, you remove salt. You need to replace it.

If you change 20% of the water (e.g., 60 gallons in a 300-gallon tank), you need to add 20% of your total salt dose back to maintain concentration.

For a 300-gallon tank at 0.3% (7.5 lbs total salt):

20% water change removes 1.5 lbs of salt
Add 1.5 lbs of salt dissolved in bucket water to replace

Use a refractometer for precise salinity measurement if you're maintaining a specific concentration. Test kits for salinity are also available. Don't rely on "it should be around 0.3%" if you've been doing water changes and re-dosing without measuring.

What Salt Can't Do - Knowing the Limits

KHV: No effective treatment exists. Salt at any concentration will not prevent, treat, or slow KHV progression. If you're using salt during a KHV quarantine, it's for osmotic support only - not treatment.

Bacterial infections: Salt at 0.3% provides mild supportive benefit for fish with bacterial infections (reduced osmotic load on damaged skin). It does not treat the infection. You need targeted antibiotics and wound care.

Gill flukes (Dactylogyrus): Salt has minimal effect on monogenean flukes. These require praziquantel.

Ich (full lifecycle): Salt at 0.5% with heat treatment (78-80°F) can disrupt ich, but it's not reliable as a standalone treatment. Combined approaches using salt, heat, and malachite green/formalin products are more effective.

Anchor worm and lice: Crustacean parasites are resistant to salt at quarantine concentrations. Mechanical removal and specific insecticide treatments are needed.

Removing Salt After Treatment

When quarantine ends or you need to transition fish to a non-salted system, reduce salt concentration gradually - the same principle as adding it.

Change 20-25% of the water every 2-3 days without replacing the salt. The concentration will drop gradually. For a fish going into a display pond with no salt treatment, allow 1-2 weeks to gradually reduce from 0.3% to near zero.

Abrupt removal of salt from a fish that's been in 0.3% for weeks can cause osmotic stress, particularly if the fish was compromised during quarantine.

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FAQ

What is the correct salt dose for koi quarantine?

Standard prophylactic quarantine: 0.3% (2.5 lbs per 100 gallons). For active parasite treatment or post-show quarantine: 0.5% (4.2 lbs per 100 gallons). Always build concentration gradually over 48-72 hours rather than adding the full dose at once. Use non-iodized salt only - iodized table salt contains additives that are harmful to koi.

When should I use salt in koi quarantine?

Salt is appropriate from day 3-4 of quarantine onward (not day 1 - let fish settle first). It's standard practice to maintain 0.3% throughout a quarantine period. Increase to 0.5% when you're seeing signs consistent with external parasite activity. Don't add salt to a system with established aquatic plants (it will kill them) or when using certain medications (some react with salt or change treatment dynamics).

When is salt treatment not enough?

Almost always in combination with other problems. Salt alone is not a complete parasite protocol - you need praziquantel for flukes. Salt is not a treatment for KHV, bacterial infections, ich in established infestations, or crustacean parasites. Think of salt as a supportive measure and osmotic aid that's part of your quarantine protocol, not the protocol itself.

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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