You learn something new everyday. I always thought raising the temp helped when curring ich. I use hypo, and q-tank, but have always been told to raise the temp a couple of degrees. I always gave this credit as I know raising the temp lowers the salinity, and figured that must be where people get the idea that raising the temp helps cure ich.
rich1515,
As far as the temp difference from 100' to 10' in a matter of seconds. In most tropical areas there's a very minimal difference. When I was diving in Hawaii the temp difference was only 1-2 degrees difference. Even when diving in colder waters I've only noticed a difference of 2-3 degrees. In freshwater I find big differences in temps, anywhere from 10-15 degrees. The fish that I observed did not go from top to bottom in that manner. They did move along the reef, but not normally to the top. They may have moved vertically up a wall, cliff, or rock, but normally only 15-20 ft.