Salt baths are the oldest known medical treatment that have been used in both aquaculture and the aquarium hobby.

Simply put, they work because the fish are more resistant to increased levels of salt then the little critters you are trying to kill.

Here's a quick howto for salt baths for your freshwater fish:

Things you need:
. Two 5 gallon buckets
. A cup or so of Doc Wellfish's Aquarium Salt
. Enough water, pre-conditioned for a complete water change for the tank.
. Stress Coat

Disclaimer: Depending on the current progression of disease and stress level of your fish, the salt bath can kill them by being too much of a shock to their system. You'll have to use your best judgement to figure out when it's appropriate to adminster this treatment. I typically won't administer to a fish who is already loosing balance and in an extreme state of distress. The earlier the stage of the disease (no matter what it is) the better chances your fish has for survival.

OK, now onto the treatment:

First fill up the first 5 gallon bucket at least 1/2 way with water from the aquarium. You'll put the fish in here after the salt bath and he'll stay there while you clean the tank.

Then put two gallons of water from the tank in your other bucket and dissolve 1/2 cup of salt (the ratio is 1/4 cup of Doc Wellfish's Aquarium Salt per gallon). Make sure that all of the salt is dissolved before you bathe the fish.  If not you burning the fish if the salt crystals come in contact with their skin, scales, or fins. Make sure that you use water taken from the tank that the fish is already in. That will help to reduce the shock to the fish.

Place the fish in the bucket for 5 minutes. GET A STOPWATCH AND MAKE SURE IT IS 5 MINUTES, NO MORE OR LESS.

It is normal if the fish floats, and ends up on its side. If it stops moving or breathing RETURN IT TO THE TANK IMMEDIATELY.

After the 5 minute bath, transfer the fish to the other bucket of fresh water from it's tank and add a bit of stress coat.

Then, completely drain the tank that he's been in and make a mixture of salt water, 3 cups for 5 gallons (something like 3/4 cup per gallon - darn salty) in very warm water with marine salt and pour that in the tank. Stir up the gravel and I soak everything from that tank in this solution (all filter medium, heater, hoses, rocks, everything) for 15 minutes,

The purpose of this step is to kill (or greatly degrade) the offending organisms in the tank.  If the salt bath will kill the buggies on the fish, but you leave them in the tank, the fish will just get sick again.

Then, drain tank, rinse everything really well with fresh water, and fill it up with pre-conditioned fresh water.

Then, slowly add fresh water to the bucket that your fish is recovering in and get him/her acclimated to the new tank water.  Once you've done this return the fish to the tank.

I'm not certain about this, but it's likely that this will kill most of your beneficial bacteria as well. As a result, you'll need to keep a close eye on the water parameters and make water changes to keep the NH, NO3, NO4 down while the fish recovers, and your good bacteria recover.

On the second day make a mixture of 1/3 cup of salt (up from 1/2 the first time) per gallon of water from the tank.

Again, bathe the fish for 5 minutes, keeping a close eye on him. The fish will likely be more boyant and float more than the previous day.

Return the fish back to his tank and do a 50% water change.

Give the fish one day of rest and then repeat the bath again at the higher salinty twice more if necessary.

When I did it, it only took twice to knock out a columnaris infection.

If you have any questions, just use the Contact Me form to send me an e-mail and I'll be happy to lend any advice that I can.

Good luck!

-- Ryan