Koi Salt Treatment Calculator: Pond Volume to Dose

By KoiQuanta Editorial Team|Updated Mar 2026

Salt dose calculations are simple math that get done wrong surprisingly often - because the pond volume number is wrong, because someone forgot to account for existing salt in the water, or because a water change diluted the concentration and nobody compensated.

This page walks you through the calculation for any pond size and any target concentration, with worked examples.

TL;DR

Includes 0.1%, 0.3%, and emergency dosing calculations with step-by-step worked examples.
If you're at 0.1% and targeting 0.3%, you only need to add the difference.
You store the tank volume in the tank profile, enter the target concentration and the current measured concentration, and the calculator returns: 1.
Grams and pounds of salt needed (incremental only) 2.
Recommended addition schedule based on the size of the concentration change 3.
Reminder to re-measure with refractometer after the final addition 4.
Multiply your pond volume in gallons by the target percentage divided by 100, then multiply by 8.34 (weight of a gallon of water in pounds).

The Formula

Grams of salt needed = Target concentration (%) × 10 × Volume in liters

Or in US measurements:

Pounds of salt needed = (Target concentration ÷ 100) × Volume in gallons × 8.34

The simpler rule of thumb that most keepers use:

0.1% = 1 lb of salt per 120 gallons (more precisely: 0.84 lbs per 100 gallons)
0.3% = 2.5 lbs of salt per 100 gallons
0.5% = 4.2 lbs of salt per 100 gallons

Step-by-Step Calculation

Step 1: Determine Your Pond Volume

If you don't know your pond volume, calculate it:

Rectangular or square pond:

Length (ft) × Width (ft) × Average depth (ft) × 7.48 = gallons

Circular pond:

3.14 × Radius (ft)² × Depth (ft) × 7.48 = gallons

Kidney or irregular shape:

Break into sections, calculate each section as a rectangle or oval, add them together.

If your pond is 12 ft × 8 ft × 4 ft deep:

12 × 8 × 4 × 7.48 = 2,872 gallons (approximately)

Step 2: Test Existing Salt Concentration

Before adding any salt, test what's already in the water with a refractometer ($15–25). If you're at 0.1% and targeting 0.3%, you only need to add the difference.

Incremental salt needed = (Target % - Current %) × 10 × Volume in liters

Step 3: Calculate Salt Amount

Example 1: New koi quarantine program tank, 0% to 0.3%

Tank volume: 300 gallons = 1,136 liters

Target: 0.3%

Salt needed: 0.3 × 10 × 1,136 = 3,408 grams = 7.5 lbs

Check: 300 gallons × 2.5 lbs per 100 gallons = 7.5 lbs ✓

Example 2: Increasing from 0.1% to 0.3% in 1,500-gallon pond

Current: 0.1%

Target: 0.3%

Incremental increase: 0.2%

Pond volume: 1,500 gallons = 5,678 liters

Salt needed: 0.2 × 10 × 5,678 = 11,356 grams = 25 lbs

Example 3: After a 30% water change on a 0.3% tank

Original: 300-gallon tank at 0.3%

Water change: 30% = 90 gallons removed and replaced

New concentration after water change: 0.3% × 70% = 0.21%

Volume still in tank: 210 gallons at 0.3% + 90 gallons at 0% = effectively 0.21% for full 300 gallons

Salt needed to return to 0.3%: (0.3% - 0.21%) × 10 × 1,136 liters = 1,022 grams = 2.25 lbs

Common Target Concentrations and Their Uses

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

| 0.1% | 0.84 lbs | 1 g/L | Stress reduction, arrival protocol |

| 0.3% | 2.5 lbs | 3 g/L | Standard quarantine, parasite treatment, nitrite protection |

| 0.5% | 4.2 lbs | 5 g/L | Active parasite treatment, bacterial skin conditions |

Salt Type Matters

Non-iodized salt only. Iodine is toxic to koi at the concentrations added to iodized table salt.

Acceptable salt types:

Solar salt (pool salt) - inexpensive, large bags, non-iodized
Non-iodized kosher salt
Non-iodized aquarium salt (most expensive, no functional advantage)
Non-iodized rock salt or water softener salt (check label - must say non-iodized)

Don't use: Iodized table salt, sea salt blends with added minerals, road salt (may contain anti-caking agents).

How to Add Salt Safely

Always pre-dissolve. Add salt to a bucket of pond water, stir until fully dissolved, then pour the solution into the pond. Dry salt landing on fish can cause localized osmotic damage.

Add in increments:

For increases up to 0.1%: single addition is fine
For increases of 0.1–0.2%: two additions at least 4 hours apart
For increases of 0.2–0.3%: three or four additions over 24 hours

The fish's ability to handle a rapid osmotic change has limits. Building gradually gives their osmoregulatory physiology time to adjust.

KoiQuanta Built-In Calculator

KoiQuanta's salt calculator is embedded in the quarantine treatment entry. You store the tank volume in the tank profile, enter the target concentration and the current measured concentration, and the calculator returns:

Grams and pounds of salt needed (incremental only)
Recommended addition schedule based on the size of the concentration change
Reminder to re-measure with refractometer after the final addition
Next salt addition calculation pre-populated when a water change is logged

FAQ

How do I calculate salt dose for my koi pond?

Multiply your pond volume in gallons by the target percentage divided by 100, then multiply by 8.34 (weight of a gallon of water in pounds). Or use the simpler rule: 2.5 lbs of salt per 100 gallons for 0.3% concentration. Subtract any existing salt concentration first - only add the incremental amount needed to reach the target.

What is a 0.3% salt concentration?

0.3% means 3 grams of salt per liter of water (3 g/L), or approximately 2.5 lbs per 100 gallons. This is the standard therapeutic concentration for koi quarantine - effective for osmoregulatory support, mild antiparasitic action against protozoan parasites, nitrite protection at the gill, and antibacterial support at wound sites. It's the target for most quarantine salt protocols.

Can I overdose my koi with salt?

Yes. While koi tolerate salt well up to 0.5–0.6%, concentrations above this cause osmotic stress that compounds other health problems. The risk isn't from a correctly calculated 0.3% dose - it's from calculation errors (usually from underestimating pond volume and then adding more salt because "it doesn't seem to be working"). Measure your pond volume accurately, calculate precisely, and verify concentration with a refractometer rather than adding salt until symptoms resolve.

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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