The Zoo Med Dr. Turtle Slow-Release Calcium Block Turtle Supplement can be used to help prevent issues as well as treat some soft shell issues. It can safely be used with hatchling turtles.
The slow-release calcium block can be used with yellow belly sliders, it will help add calcium to the water which they will consume when drinking. However, Zoo Med does not recommend using a calcium powder when feeding them as it can just foul the water. Make sure they are being fed a balanced pelleted diet with added vitamins and minerals.