(Source: Sourceaquariacentral.com)
It's important to note that Ichich is always present, and there is nothing you can do to get rid of it. Fish are naturally immune to Ichich, and only succumb to it when their immune systems or protective slime-coating have been compromised, or when they're stressed.
This is why you will commonly see fish contract Ichich after traveling, if they're being bullied by other fish, and when they're living in poor water conditions. Also, if you have a fish like a PlecostomusH. plecostomus (also known as pleco), Loachloach, or certain catfishes, they will actually attach to other fish, and "bite" off their slime coating, exposing them to Ichich.
Finally, just like if you moved a person sick with the flu into a house full of healthy people, introducing a fish with Ichich into an established aquarium is a bad idea. And just like giving a healthy person flue medicine, giving healthy fish Ichich medicine isn't a good idea.
For freshwater fish, Ichich can be treated in several different ways:
Chemical Treatmenttreatment: Somethingsomething like Ich Attack or ParaGuard are two that I personally recommend. Follow the directions on the bottle, it'll tell you how much to put in per gallon, and how often. Be careful, these two shouldn't effect anything else in your tank, but with chemical treatments you always run the risk of throwing off the chemical balance (usually PhpH levels). Copper-based treatments like CopperSafe, while effective, are also really bad for invertebrates, like shrimp and crayfish. I would suggest avoiding copper if you have invertebrates in your tank.
Aquarium Saltsalt: Addingadding aquarium salt to the water helps calm fish, providing them with certain nutrients, and removesprotects fish from nitrites via blocking gill absorption of nitrites, helping fish to absorb more oxygen. I wouldn't recommend using aquarium salt with PlecostomusH. plecostomus in the tank, as they can be sensitive to it, though some people have no problems. Also, aquarium salt is special,special; don't use other kinds of salt.
Temperature: Raisingraising the temperature to about 86 degrees Fahrenheit (30 degrees Celsius) will create an environment that the fish can survive in, but not the parasite. Don't leave the temperature at that though, as it will stress the fish out to be in there for long. It's all about who can survive it longer.
Aquarium Saltsalt and temperature: I prefer this option as the salt helps the fish through the temperature rise more. Again, think twice about salt and Plecosplecos.
In a quarantine tank, us chemical treatments on the fish. Since you're treating the fish in a quarantine tank, you can use copper-based treatments like CopperSafe. I have not had the guts to try it, but according to the bottle, Ich Attack is reef safe. Meaning you should be able to use it in a tank with corals in it without killing the corals. I'm not going to say you shouldn't do anything like that, but I don't want to take responsibility for anything like that.
AAn UV sterilizer will help remove some of the parasites from the water. I've never used one, so I can't say much about them. They're expensive, and if you have the money for one, I think they'd be nice to have.
On top of the treatment, I would perform gentle water changes. Something like 10% every 5 days. Enough to take out a good chunk of the old water, but not enough to stress the fish anymore than necessary. Have a bucket of water prepared the day before with something like [Seachem Prime][18] for freshwater fish. For saltwater fish, use pre-mixed saltwater already heated to the right temperature to avoid any drastic changes.
On top of the treatment, I would perform gentle water changes. Something like 10% every 5 days. Enough to take out a good chunk of the old water, but not enough to stress the fish anymore than necessary. Have a bucket of water prepared the day before with something like Seachem Prime for freshwater fish. For saltwater fish, use pre-mixed saltwater already heated to the right temperature to avoid any drastic changes.