Salt Calculator
Enter your pond volume and current salt level, then any one of the last two — the remaining box fills itself.
Use pure, additive-free salt (no iodine, YPS, or anti-caking agents). Add it straight to the pond — broadcast it across an area of strong water movement, such as a return jet, waterfall or aerator, so it disperses as it dissolves. Salt does not evaporate — only replace what you lose to water changes, splash-out, or backwashing, which is why your current reading matters. Levels above about 0.3% will kill most submerged pond plants, and salt should not be combined with certain medications. Not sure of your pond volume? Use our Volume Calculator first. Always measure with a salinity meter rather than relying on dosing math alone.
Related pond calculators
How much salt does a koi pond need?
Roughly 8.35 lb of salt per 1,000 gallons raises salinity by 0.1%. That single figure is the whole calculation — everything else is multiplication. For a 3,000 gallon pond going from nothing to 0.3%, that is about 75 lb.
The three levels people normally work to:
- 0.1% — a low background level. Mild, well tolerated indefinitely, and enough to give useful protection against nitrite.
- 0.3% — the usual working level for parasites and for supporting stressed or damaged fish. Most submerged plants will not survive it.
- 0.5% — short-term only, and not somewhere to leave a pond sitting. Watch the fish closely at this level.
Salt does not evaporate — and that catches people out
Water leaves your pond constantly through evaporation. Salt does not go with it. Top the pond up with fresh water and the salt that was already there is still there, now in a slightly smaller volume, so the concentration actually creeps up rather than down.
The only ways salt genuinely leaves are water changes, splash-out from a waterfall, and backwashing a filter. This is exactly why the calculator asks for your current level rather than assuming you are starting from zero. Dosing a pond to 0.3% when it is already sitting at 0.25% is a very different amount of salt from dosing it from scratch — and people who re-dose from scratch every time are how ponds quietly end up at 0.6%.
How to add salt to a koi pond
Add it straight to the pond. Broadcast it across an area of strong water movement — a return jet, a waterfall, or over an aerator — so it disperses as it dissolves rather than settling in one spot. Never tip it in a heap where fish rest on the bottom.
Use pure, additive-free salt. No iodine, no yellow prussiate of soda, no anti-caking agents. Solar salt, pool salt and food-grade salt are all fine provided the bag lists nothing but sodium chloride.
Add it over a day or two rather than all at once, especially if the pond is already stressed, and run your aeration while you do it.
What salt actually does, and what it does not
Salt helps fish with osmoregulation — it narrows the gap between the fish and the water around it, so a damaged or stressed koi spends less energy simply holding itself together. That is why it is used to support fish through illness and handling. It also gives real protection against nitrite toxicity, because chloride competes with nitrite for uptake across the gills.
What salt does not do is fix ammonia. It does nothing to a broken or undersized biofilter, and it will not clear a reading on a test kit. If you have ammonia, run the number through the free ammonia calculator and deal with the cause. Salt is also not a universal parasite treatment — it handles some and not others.
Common questions
How do I lower the salt level in my pond?
Water changes, and only water changes. There is no product that removes it and it will not fade over time. Swapping out roughly a third of the water lowers the level by about a third. Do it over several days rather than in one go, and match the temperature of the replacement water.
Will salt hurt my pond plants?
Above about 0.3%, most submerged and marginal plants will die. Water lilies are more tolerant than many but not immune. If you value the planting, either treat at 0.1% or move the fish to a treatment tank instead of salting the whole pond.
Do I need a salinity meter, or will test strips do?
Get a meter. Salt strips are coarse and easy to misread, and the difference between 0.3% and 0.5% matters. A meter is inexpensive next to the cost of guessing, and it is the only way to know your real starting point before you add more.
Can I use salt at the same time as other treatments?
Check the label of whatever you are using first. Some medications specifically warn against being combined with salt, and some become harsher in salted water. Where a product label and any calculator disagree, follow the label.
How long can I leave salt in the pond?
0.1% is a level a pond can sit at indefinitely. 0.3% is a treatment level, not a permanent state, and it is worth bringing back down once whatever you were treating has resolved. 0.5% is short-term only. Leaving a pond permanently salted also means your biofilter and plants adapt to it, so decide which you are doing rather than drifting into it.
What if I have already added too much?
Enter your actual current level and your intended target in the calculator above and it will tell you roughly how much water to replace to come back down. Do it gradually.
