In the case of a heavy outbreak, white spots will be visible. Most if not all internal parasites prefer the gills. The fish's gills are not protected with a slime coat, and furthermore they are rich with blood. Many fish are resisitive to ich, and almost all fish will build up some immunuty if faced with repeated attacks. With healthy fish, it is not uncommon for ich to never show up externally, but it will continually cycle through the three stages of life, and attach in the gills. This is precisely how ich hides for months or even years and then shows up as soon as something else stresses the fish. Since flashing is one of the most common symptoms, it is usually cause for concern.
I still think amonia should be checked first, and it is necessary to know if chloramines or chlorine are in the water supply. The flashing is predominant right after water changes and this does lend to improperly treated chloramines to some degree. I would only treat for ich after water conditions are verified as good.
If you are unable to find out whether or not Chloramines are in use, my reccomendation is to buy a bottle of "prime" water conditioner and use that exclusively. It will break the Chloramine bond and detoxify the ammonia that is left. If you switch to prime and the symptoms still occur after a few days I'd go the next step and treat for ich.
There are of course a lot of variables and possibilities when flashing is the only sign of a problem. Attack the most likely ones sytematically and take you time to make sure one thing is eliminated before starting to work on the next step. This will be easier on your fish and also when you do stop the problem you can be reasonably sure of what it was. If ammonia burn is the problem and you add salt and raise temps it will do more to harm than help things. However if you start by elimanating ammonia as a possible problem then you can go on to the next most likely and so on.
I have not kept White clouds, but As a general rule the concern with raising temperature is the oxygen level available. The warmer the water the less oxygen it carries. Most cold water fish require high oxygen levels. Normally if I am raising temperatures on any oxygen sensative fish, I just increase surface turbulence and circulation. Remember that the salt will kill the ich no matter what, raising the temp speeds up the life cycle of ich and therefore shortens the treatment period. Ich can be treated without the temperature increase it just takes much longer.
Dave
