my black widow tetras have got little white spots on them, i take it that is white spot, i went to my lfs and bought white spot treatment. we were told to take out the black carbon part of the filter out, then put the solution in the water, and not do a water change until the spots have gone, is that right? can anyone suggest anything different, how often do we need to use the solution, we are understanding it as just the once? that right to? ???