well mate i will try to help you out here with what i know regarding itch, it is then up to you to try to identify the disease by the symptoms.
Firstly this is a parasitic infection that infects the fins, gills and body of the fish.
The first symptoms noticed are randomly distributed white spots over the fishes body, it is now easy to distinguish from CORAL REEF DISEASE (Amylodinium ocellatum) and SALT WATER ITCH (cryptocaryon irritancy) from the size of the spots.
Itch is recognizably by the size of the spots, and with this disease the spots are about the size of salt crystals, with Coral Reef Disease the fish appears to have been dusted with fine white powder.
With Itch your fish may display the following symptoms,
Rapid breathing, lack of appetite, tendency to rub themselves on the rocks and substrate, and they will move from their familiar haunts and aggregate in a spot of high water turbulence.
This is all caused by a nasty little ciliated protozoan that has a very similar life cycle to the nasty that causes Coral Reef Disease.
When these protozoans mature on the fish, they then drop to the bottom of your tank and encyst, while encysted, free swimming parasites develop and are released into your tank to then infect the other fish in there..
TREATMENT. You will need a free copper or ionic copper based medication and make sure that the active ingredient is copper sulphate, copper pentahydrate or other copper compounds.
You now need to add the proper amount of copper solution to your quarantine tank as per the label instructions until you get a concentration of 0.12 to 0.18 mg
You will need to monitor your tank on a daily basis to make sure that the levels do not exceed or decrease beyond the advised medicated levels.
You will need to treat and monitor your fish for a MINIMUM of 21 days before release back into you display tank.
Mate i hope this information helps you..