Yeah, we definitely need more information to be able to help you. Whitespot should not be fatal, not when being treated, so I strongly suspect that there is an underlying factor (ie ammonia) that has caused the whitespot and also the deaths. Protozin is pretty effective on most strains of whitespot. When that doesn't work, we generally recommend copper sulfate (Coppersafe) but if the fish are stressed due to something else, killing the whitespot parasite may not save them.
When fish are stressed, they get sick very easily and come down with whitespot etc. Treating for the illness does not remove the stressor, and that's why sometime fish die anyway if the cause of the stress is not removed.
Tank size, how long has it been set up, how was it cycled. Please tell us exactly what's in it (species and number of each that you had before, and also what's left.)
The most helpful thing you could give us would be water parameters (ammonia/nitrite/nitrate/pH/temp). Do you have a test kit?
