How Much Salt to Add to a Koi Pond: The Complete Dosing Guide

By KoiQuanta Editorial Team|Updated Mar 2026

The therapeutic salt concentration for koi parasites is 0.3%, which equals 2.5 pounds of salt per 100 gallons of pond water. That's your baseline. Everything else, how much to add, when to top up, how long to run the treatment, follows from that number.

This guide covers the full koi pond salt treatment calculation, when to use different concentrations, and how KoiQuanta's treatment progress tracker keeps the program on track from day one to clearance.

TL;DR

At this concentration, salt treatment is generally limited to 3–5 days maximum.
Koi can tolerate 0.5% short-term but prolonged exposure causes osmotic stress.
A 25% water change removes 25% of your salt.
If the label says "pure sodium chloride" or "99%+ NaCl," you're good.
At 0.3% therapeutic concentration: approximately 0.025 lbs of salt per gallon, or roughly 1.1 ounces per gallon.
Rock salt is suitable for koi pond treatment as long as it's predominantly sodium chloride (99%+ NaCl).
For a standard 0.3% parasite treatment, maintain the concentration for 2–3 weeks.

Direct Answer: How Much Salt for a Koi Pond

At 0.3% concentration: 2.5 lbs of salt per 100 gallons (or 25 grams per 10 litres)

So for common pond sizes:

500 gallons → 12.5 lbs of salt
1,000 gallons → 25 lbs of salt
2,500 gallons → 62.5 lbs of salt
5,000 gallons → 125 lbs of salt

Use pure sodium chloride (NaCl), non-iodized. Pool salt, water softener salt (check the label for purity), or dedicated pond salt all work. Iodized table salt can harm koi at treatment doses.

Salt Concentrations and What They Do

0.1–0.15% (1–1.5 lbs per 100 gallons)

A mild tonic dose. Reduces osmotic stress on koi with compromised gill or skin barriers. Used during recovery from trauma or surgery, not for treating active parasite infestations.

0.3% (2.5 lbs per 100 gallons)

The standard therapeutic dose for most external koi parasites. Effective against Chilodonella, Trichodina, Costia, and Ich. Creates sufficient osmotic pressure to suppress parasite reproduction without stressing koi. This is the most commonly used treatment concentration.

0.5–0.6% (4–5 lbs per 100 gallons)

A higher therapeutic dose sometimes used for severe infestations or stubborn parasites. At this concentration, salt treatment is generally limited to 3–5 days maximum. Koi can tolerate 0.5% short-term but prolonged exposure causes osmotic stress.

Above 0.6%

Used only as a brief dip (2–3 minutes), not a pond treatment. At these concentrations, salt is acutely toxic to most parasites, but also stressful to fish. Pond-wide treatment at this level is not appropriate.

How to Add Salt to a Koi Pond

Don't dump it all in at once. Large rapid changes in salinity stress koi, particularly those already weakened by illness.

Step 1: Calculate your target dose based on current pond volume at operating water level.

Step 2: Dissolve salt in a bucket of pond water before adding it to the pond. This prevents localised high-concentration zones.

Step 3: Add one-third of the total dose. Wait 2–4 hours. Add the next third. Wait again. Add the final third.

Step 4: Measure salinity 2–4 hours after the final addition using a refractometer or salt test kit. Confirm your target concentration was reached.

Step 5: Log the treatment start date, dose added, and measured concentration in KoiQuanta.

How Long to Run Salt Treatment

At 0.3%, a full parasite treatment course runs 2–3 weeks. The lifecycle of external parasites means that a single treatment doesn't eliminate all life stages simultaneously, you need to maintain therapeutic concentration long enough to catch hatching cysts and new infections.

Generic salt calculators online give you a dose but can't track your treatment progress. KoiQuanta calculates and logs your full salt program, showing remaining treatment days and flagging when a water change will drop your concentration below the therapeutic threshold.

When to Do Water Changes During Salt Treatment

You don't avoid water changes during salt treatment, but you plan them.

Every water change you do during a salt treatment removes a proportional amount of salt. A 25% water change removes 25% of your salt. Before any water change during an active salt treatment, use KoiQuanta's water change impact calculator to calculate exactly how much salt to add back afterward.

The salt top-up formula: top-up dose = pond volume after change × target concentration − post-change concentration.

Don't skip the water changes. Rising nitrates and ammonia spikes are treatment killers. Just compensate for the salt you remove.

Can I Use Rock Salt?

Rock salt (sodium chloride with some mineral impurities) is generally fine for koi pond treatment at therapeutic concentrations. The mineral content is low enough not to cause problems.

What you want to avoid: iodized table salt (iodine is toxic to koi at high doses), and salts with anti-caking agents or flow agents (some contain compounds that aren't koi-safe).

If the label says "pure sodium chloride" or "99%+ NaCl," you're good. If it lists additives beyond trace minerals, check what they are before using it.

How much salt per gallon for koi treatment?

At 0.3% therapeutic concentration: approximately 0.025 lbs of salt per gallon, or roughly 1.1 ounces per gallon. For the most accurate calculation, use KoiQuanta's salt dose calculator with your exact pond volume, the per-gallon figure is just a quick reference. Confirm your actual concentration with a refractometer after adding.

Can I use rock salt or does it need to be pure sodium chloride?

Rock salt is suitable for koi pond treatment as long as it's predominantly sodium chloride (99%+ NaCl). Avoid iodized table salt, iodine accumulates in pond water and can harm koi at treatment doses. Also avoid salts with listed anti-caking agents or other additives unless you've confirmed they're koi-safe. Pool salt and water softener salt (check label) are both commonly used and generally appropriate.

How long do I leave salt in my koi pond?

For a standard 0.3% parasite treatment, maintain the concentration for 2–3 weeks. Shorter treatment periods may fail to catch all lifecycle stages of the target parasite. At the end of treatment, reduce salt gradually through water changes rather than doing a single large dilution. KoiQuanta's salt treatment tracker shows remaining treatment days and calculates the water changes needed to safely reduce concentration at the end of the program.

Koi Parasite Treatment: Complete Protocol Guide

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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

Track Your Salt Treatment in KoiQuanta

The salt dose calculator handles the initial dose calculation. The treatment progress tracker manages everything after that, logging daily observations, scheduling water changes, and flagging retreatment needs.

Start your free KoiQuanta trial and run your first salt calculation today.