Since itch is very common fish disease it's treatment methods are widely common and effective. Whenever you found symptoms of itch on your fish which i have told in previous topic you should immediately take a steps for treatment, it because it is extremely communicable and fatal disease.
Treatment :
Most Basic :
The itch is life cycle is temperature dependant. On raising temperature itch cycle speeds up and on further increasing temperature to 30 C/86 F, stops the itch reproduction cycle and on further increasing temperature to 32 C/90 F, the itch starts dieing. But it is extremely important to see that your fishes can tolerate that amount of temperature. So if you are having tropical fishes which are temperature resisted you can try this. Also it is important to see that on high temperature metabolism rate of fishes increases and they require more oxygen. So increase aeration in your tank. This method is sometime adopted with salt method.In salt method some amount of aquarium salt is added to the tank. The quantity is 1 teaspoon of salt per 4 litres or 1 gallon. There are controversies regarding use of table salt(iodized). Some people says that it can be used for treatment but some says it doesn't. Also keep in note that you should no use this method with scaleless fishes like cat fish because their skin is very sensitive.
So raise the temperature to given value and add the required amount of salt .And keep the temperature up to week.And keep changing 1/4 amount of water daily.
Note:Do not change temperature instantaneously.1 c/2 f in 4 hrs till it reaches the specified marl.
Also do not add salt crystal first dissolve salt in other container then add that solution to tank .
Other method:Use of medication
You can go to pet store and ask for medication for itch treatment. The medication which are available are malachite green, methylene blue, quinine hydrochloride etc are easily available. You can use as prescribed on them or by the dealer. Raise the temperature to increase rate of life cycle.If you have scaleless fish cut the dosage to half. Discontinue carbon filtration as it remove chemicals. Perform treatment for 10 to 14 days even after itch is removed.
Precaution:
1. Do not add any thing from tank which was infected by itch before treatment.
2. Put newly bought fish in quarantine tank for 2 weeks to check for any sign of any disease.
3. Maintain good water quality .
4. Avoid any kind of stress to your fish.
5. Give a good diet to fish rich in vitamins and minerals.