rock salt for fish tanks

How to Use Salt in Fish Tanks and Ponds

Salt Against Ciliates

rock salt for fish tanks
Rock salt can sometimes be used in ponds and fish tanks

I recommend that you use salt, before you try anything else for parasites. I recommend salt so often because it has so many benefits over other medicants.
1) It does not harm the majority of fish species.
2) It does not (usually) push sick fish “over the edge.”
3) It eliminates, QUICKLY, 6 of 9 parasites I can easily recall.
4) It does not get bound out of the system by organics or sunlight. (Like formalin)
5) It does not pose a health risk to humans contacting it. (Like formalin)
and 7) It WON’T harm your filter!

Salt: Remove submerged plants. Perform a fifty percent waterchange, and clean the pond as well as reasonably possible without causing undue delay in treatment.

Apply one teaspoon of non iodized table salt per gallon of water every 12 hours for three treatments (Total dose: 3 tsp per gallon).

Alternatively, for larger systems, dose one pound per hundred gallons of water every 12 hours for three treatments (3 pounds per hundred gallons).

Add all at once in the case of epidemic mortality.

Salt is a superior remedy for many different reasons, many of which will show up in a search of this website and in the book I extoll this remedy even more.
Kosher salt, Sea Salt, Non-Iodized Table, Rock and Ice Cream Salts are acceptable. Do not use salt intended for livestock if it contains any minerals or trace elements.

Caution! No YPS or Yellow Prussiate of Soda should be in the salt. Prussic Acid is hazardous to fish because it dissociates into Prussic Acid in water! Prussic acid can drop the pH in soft water systems.

Add the salt all at once if fish are dying off rapidly.
But if the losses are a little slower, it’s easier on the fish to add it in thirds.

Add one pound per hundred gallons, per day, for three days if fish are merely sick. This avoids occasional filter-shock. (2-3 day nitrite spike)

Salt will not harm hardy Lilies, common Papyrus, or Irises. Will cause yellowing of Hyacinths, Celery and Water Lettuce
But salt will kill Anachris, String Algae, Cabomba and Elodea. Live plants can be killed or yellowed by this, so be careful to remove these before treatment. As a general rule, plants with a defined root system will usually survive salting, while floating varieties like Anachris, Cabomba and Wisteria are flatly killed. My Apons died back 50%, Cryptocoryne couldn’t care less, Pennywort hated it but did not die, Anubias yellowed and recovered, in the ponds, Lilies yellow marginally but do not even stop flowering. Iris is impervious, and Hyacinths hate it but they only yellow in the older leaves, and bounce right back.
Pull sensitive plants to baby-pool and treat with Formalin in this. (25 ppm 8-12 hours)

3 pounds per hundred gallons = 0.3%
6 pounds per hundred gallons = 0.6%

Leave salt in the pond for 14 days minimum, then remove by partial water changes over subsequent weeks.

Note From Doc Johnson
“I am always absolutely sure to read every ingredient in the salt I am using. I do NOT take it for granted tha my time honored favorite brand of salt is still being made with the SAME anti-caking agent as always. They *do* change these ingredients occasionally and the addition of Yellow Prussiate of Soda (YPS) can cause death fairly rapidly (through pH crash) in soft water!” ~ Doc Johnson

Update on salt…
Astor, Akso Nobel, or Morton brand non-iodized salts sufficient to treat one system to 0.3% two times. Most any salt is okay if it’s not: YPS laced, mineralized, iodized*, or really dirty. I’ve used animal feed or licks – “salt blocks” from the feed store with excellent results, you need to read labels and look for 99.5% purity with no trace minerals. The blocks are easy to store and transport. Put them in the way of the water return and they dissolve rapidly. NEVER put salt into the filter intake. The sudden rise in salinity will annihilate your filter bacterial function. One man local to me put fifty pounds into his skimmer, straight through the filter, and made his beads snow white.

*What’s the “scoop” on iodized salt; is it toxic or not?

Not toxic to fish. Very likely, the first few times it was used with smaller filtration systems in higher amounts, Iodized salt set the filter back causing an ammonia situation to arise. It was *theorized* that the bacterial stumble was caused by the iodine/betadine effect.

Is there a way to measure the salt once added?
Yes, there are electronic salt meters which are accurate, easy to use and surprisingly cost effective. Saltmeter (for availability) – check out the where to buy section of this web site. (

What can salt do for me?

Salt kill list: at 0.3% :
Ichthyophthirius (72 hours at tropical temperatures)
Chilodinella (24-36 hours)
Costiasis (Ichthyobodo necatrix) 60% of the time.
Almost every single Trichodiniid/Tripartiella organism.
Glossatella (24 hours irregardless of temp)
Scyphidia (24 hours irregardless of temp)
Epistylis (24 hours irregardless of temp)
Trichophrya (24 hours irregardless of temp)
External Tetrahymena
Inhibits trematode reproduction, clears 30% of adults. (Use Prazi instead)
Inhibits Lerneiid reproduction (But does not clear Lernea or argulus.) (Use an Insect-Growth-Regulator Instead.)

Is there a type of fish to be careful with?

Salt has been reported in some instances to cause health problems for the following fish:
1. Wild caught Discus. (Captive born specimens have no problem at all.)
2. Some Brokis britskii catfish
3. Otocinclus
4. Rafael Catfish
5. Ram Cichlids
6. Neon tetras
7. Cardinal Tetras
8. Tiger Barbs and Sharks die suddenly if chased with a net while salted.
Note. The divided dosing schedule has alleviated alot of these problems, but use salt at your own risk in these cases. Sometimes the numbers of fish you have from these groups make them somewhat ‘expendable’ in the interest of saving the other fish.

How long do I leave it in the water?
Fourteen to 21 days may be required to totally eradicate certain parasites at certain temperatures. Rest assured, it could stay in the water forever (not cool). But for Ich it could also be removed within seven days and recurrence of Ich would be unlikely if temperatures during treatment were around eighty degrees F. Ten to fourteen days is suggested ‘for best results’ with Ich.

Removal is by simple partial water changes. Be careful that the effluent water is not wasted onto a precious Japanese Maple or your Dad’s best Bermuda grass as it could do it some damage.

I traditionally use salt for most protozoan parasites, especially Ich, and the wholesalers/retailers who rely upon it have thanked me for the tip.

To name just a few, Suburban Water Gardens, Blue Ridge Hatchery, One of Kind Koi, Willow Pond, Finn’s Aquatics and Marine Life all provide superior fish to their retailers through the use of 0.3% salt in all freshwater species but their most sensitive South American imports. I use salt because so many other medications for Ich are caustic to the fish, reduce dissolved Oxygen levels, and can tend to disable the filter bacteria that remove Ammonia.