I found this on KoiVet.com
Salt - Sodium Chloride for Parasites
Written by Dr. Erik Johnson
Thursday, 03 April 2008 21:57
Salt can be used in freshwater systems by adding one teaspoon of salt to each gallon of water every twelve hours for three treatments. You are gradually increasing the salinity to a level of 0.3% or three teaspoons per gallon total. The dose goes in gradually over 36 hours to avoid shocking the filter (especially Nitrobacter, which results in a short Nitrite surge). Some sensitive fishes will also do better when salted if it's added so gradually. Salt should be of the non-iodized table salt variety, or an Aquarium salt recommended by the Pet Shop. 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.
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. You can get one from PondRx.com - check out the where to buy section of this web site.
What can salt do for me?
Salt at 0.3% is credited with the clearance of the following:
Ichthyophthirius (72 hours at tropical temperatures)
Chilodinella (24-36 hours)
Costiasis (Ichthyobodo necatrix)
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.
Inhibits Lerneiid reproduction