Koi Salt Dose Calculator: Precise Treatment Concentrations Every Time

By KoiQuanta Editorial Team|Updated Mar 2026

Salt is probably the most commonly used treatment in koi keeping, and it's also one of the most commonly gotten wrong. Not because the math is complicated, but because most people calculate it as though they're starting from zero salt every time. They're not.

Here's the problem that KoiQuanta's salt dose calculator solves. If you did a 20% water change impact calculator last week and topped up with dechlorinated tap water, your salt concentration dropped. If you added a half-dose during quarantine, you have some salt but not a full therapeutic level. Adding a "full dose" on top of existing salt pushes you over your target. In the worst case, it causes osmotic shock and kills the fish you were trying to treat.

The incremental dose calculation in KoiQuanta accounts for your current salt concentration and tells you exactly how much to add to reach your target, not how much you'd need in a completely empty pond.

TL;DR

Salt at 0.3% requires approximately 2.5 pounds per 100 gallons, or about 50 pounds for a 2,000-gallon pond starting from zero.
Adding salt on top of existing salt without accounting for current concentration is one of the most common errors in koi treatment.
A 25% water change removes 25% of your existing salt concentration, which must be replaced to maintain a therapeutic level.
Salt should always be added in three increments over 24-48 hours to prevent osmotic shock.
Salt concentrations above 0.5% can stress koi; concentrations above 1% can be fatal.
The KoiQuanta salt calculator accounts for current salt concentration and pond volume so each calculation gives the actual incremental dose needed.

What Salt Actually Does for Koi

Before getting into doses, it's worth understanding why you're adding salt at all. Salt at low concentrations (0.1-0.3%) works in a few ways. It reduces the osmotic stress on fish by bringing external salinity closer to the fish's internal body fluids, which makes it easier for damaged or stressed fish to maintain fluid balance. At therapeutic concentrations (0.3%), it's also directly toxic to many parasites, particularly ectoparasites like Costia and Trichodina, while being safe for koi.

Salt isn't a cure for everything. It doesn't treat bacterial infections effectively at these concentrations, and it's not appropriate for all situations. But it's one of the safest tools in the kit when used correctly.

Understanding Concentration Percentages

0.1% salt means 1 gram of salt per liter of water. 0.3% means 3 grams per liter. In imperial terms, a 0.3% concentration works out to approximately 2.5 pounds of salt per 100 gallons.

The target concentration depends on what you're treating:

0.1-0.15%: Stress reduction, mild disease prevention during spring startup or after shipping
0.2%: General parasite treatment, appropriate for ongoing quarantine
0.3%: Therapeutic antiparasitic treatment, most effective against Costia and Trichodina
Above 0.3%: Not recommended for standard pond treatment; can stress koi

The Incremental Addition Rule

Never try to reach your target salt concentration in a single addition. Always add in increments over several hours, especially if your fish are already stressed.

The reason is osmotic shock. A sudden large jump in salinity stresses koi even at concentrations that would be perfectly safe if reached gradually. Adding to reach 0.3% is fine. Dumping 0.3% worth of salt into a pond that has no salt causes a rapid osmotic shift that stresses or kills fish, which is the opposite of what you're trying to achieve.

The standard approach is to split the total dose into three additions over 24-48 hours. Calculate the full incremental dose needed, then add a third, wait 12-24 hours, add another third, and repeat. Watch fish behaviour throughout. The salt treatment guide covers the full protocol including timing and what to watch for.

How the KoiQuanta Salt Calculator Works

Open the salt dose calculator in KoiQuanta. Your pond volume is pre-populated from your profile. Enter your current estimated salt concentration (or zero if you haven't added salt recently), and your target concentration.

The calculator outputs two numbers:

The total salt needed to raise from current to target concentration
The recommended per-addition dose if splitting over three increments

It also flags if your target concentration is above the recommended range for koi or if you're already close enough to your target that adding more may be unnecessary.

After you add the treatment, log it in KoiQuanta. The system updates your estimated current salt concentration so that future calculations, including water change planning, work from the correct baseline.

Planning Water Changes Around Salt

One thing people often forget is that salt doesn't evaporate. Top-up water for evaporation doesn't change your salt concentration because you're replacing water, not salt. But a water change dilutes salt along with everything else.

A 25% water change removes 25% of your salt. If you're maintaining a 0.3% therapeutic level, a 25% water change drops you to approximately 0.225%. You may need to add salt back after large water changes to maintain therapeutic concentration.

The KoiQuanta water change impact calculator handles this automatically. Enter your planned water change percentage and it tells you how much salt you'll need to add back to return to your target level.

Frequently Asked Questions

How much salt do I add to reach 0.3% in my koi pond?

At 0.3%, you need approximately 2.5 pounds of salt per 100 gallons of pond water. For a 2,000-gallon pond starting from zero salt, that's roughly 50 pounds total, added in three increments over 24-48 hours. The KoiQuanta salt calculator determines this from your stored pond volume and adjusts for any salt already present in the water so you're adding only what's needed to reach the target.

Can I add too much salt to a koi pond?

Yes. Salt concentrations above 0.5% can stress koi, and concentrations above 1% can kill them. The bigger risk for most hobbyists is adding a full dose when some salt is already present from a previous treatment. The incremental dose calculation in KoiQuanta prevents this by accounting for your current estimated salt concentration before calculating the addition needed.

How long should I maintain salt treatment for koi?

For antiparasitic treatment, a 0.3% salt concentration is typically maintained for 7-14 days. For stress reduction during quarantine or disease recovery, lower concentrations of 0.1-0.2% are maintained throughout the quarantine period or until the fish is fully recovered. Always plan a water change to reduce salt levels when the treatment period ends, particularly before any treatments that interact poorly with elevated salinity.

How do I measure my current salt concentration in a koi pond?

A refractometer calibrated for freshwater or a dedicated pond salt meter gives the most accurate reading. Salinity test strips are a lower-cost option but are less precise. Measure from several points in the pond after running circulation for at least 30 minutes to ensure an even reading. Log the reading in KoiQuanta so the salt calculator can use it as the baseline for your next dose calculation rather than assuming you are starting from zero.

Does salt evaporate from a koi pond?

No. Salt does not evaporate. Topping up evaporated water does not change your salt concentration because you are replacing water only. A water change dilutes salt along with everything else. For every 10% water change, you remove approximately 10% of your current salt concentration and may need to add salt back to maintain therapeutic levels. The KoiQuanta water change impact calculator shows exactly how much salt a planned water change will remove.

Can I use table salt or rock salt in my koi pond?

Use only non-iodized salt specifically intended for pond use or pure sodium chloride without additives. Iodized table salt contains iodine that can be harmful to fish and beneficial bacteria at pond concentrations. Many road salts and water softener salts contain anti-caking agents or other additives. Pond-grade salt or pickling salt are the appropriate options.

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Koi Quarantine Salt Treatment: Concentrations, Dosing, and Limits

Sources

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

Get Started with KoiQuanta

Getting salt doses right requires knowing your current concentration, not just your target. KoiQuanta's salt calculator accounts for your existing salt level, pond volume, and planned water changes so every dose is calculated from your actual baseline. Try the calculator for your next salt treatment and see the difference precise incremental dosing makes.