Ich is a ciliated protozoan that can kill smaller koi by damaging their gills. It can be a real irritant to larger koi and can cause secondary bacterial infections. You will see small white spots on the scales of the fish caused by the Ich parasite under the scale in tropical fish and goldfish. These parasites go through a life cycle that averages about two weeks in duration. Other diseases can cause the appearance of white spots too, so you can’t always be sure that you are looking at Ich. Those white spots so well associated with Ich seldom if ever show up on koi infected by Ich. Under the microscope, Ich looks like a large, slowly rotating ball with a “U” shaped nucleus inside. Ich encysts under the epidermis layer of the skin of the fish. It will live there, depending on the water temperature, for up to five weeks in cold water. Medicating the pond to kill the Ich will not affect the parasite until it ventures out from under the skin to reproduce. At that time, salt at .4% will easily kill it. Thus, you need to salt the pond for an extended period to kill Ich effectively.
Treatment Procedure with Salt
Salt, when used to treat for Ich, should be added at a rate of 1 pound per 100 gallons of water each day until the pond reaches .4% salt. If there is no salt in the pond, this will take four days to reach .4%. A 1000 gallon pond will require 40 pounds of salt to achieve a salt level of .4%. This may sound like a lot of salt, but if you add it over four days, it will not bother the fish or the filter. Leave the salt level at .4% for at least three weeks. Ich is easily killed with salt when it comes out from under the fish’s scale to reproduce. However, it’s life cycle is such that it could take up to three weeks to come out and be exposed to the salted water. You can purchase 50-pound bags of solar salt at Home Depot for around $5.00 each. Use the cheapest salt you can find, as it will have no additives in it which could be harmful to the koi.