white spots can be a number of things bacteria, fungal infections or even parasites. i treated for ich not long ago when i bought an american eel they sell as bait, it turned out the ich cleared up but i had to also treat him for hole in the head. >bummer< but he is doing better now.
i like and have used "copper safe", it treats many kinds of diseases. it is made by mardel company.
one main thing i wanted to say and the reason im posting is fish hide when they are sick, they hide under wood/rocks/plants anything or anywhere you wldnt think of looking. i would suggest that you move things around slowly as not to stress the tank any more than it already is, chances are if you go in and look for the missing fish they will float to the top, and my suggestion is to get ANY dead fish out of the tank as soon as you notice that it's missing,.
i also have found if i keep my tanks at a high range of heat it helps burn off ich and it will slow down growth of ich above 78 degrees,. i keep my tanks at 80 degrees,. maybe this might help a-little,. good luck
knowy