Turtles kept in aquariums that have “hard” water from the tap will sometimes develop a whitish scale on their shells. When the turtles climb out of the water to bask and the water on their shell evaporates, the dissolved minerals and salts that are in the water are left behind in the porous areas of the turtles’ shell. As these deposits build up over time, they can eventually reach a concentration that starts to turn the shell a whitish color. The best remedy for dealing with mineral/salt buildup is to lightly brush your turtles shell with a diluted vinegar solution once a month to remove the whitish film of minerals and salts.