How much water should i put in my baby painted turtles tank?

so i have a baby painted turtle and he is only about the size of a half dollar and he lives in a 10 gallon tank. he is my first turtle and i want to make sure hes happy. i have rocks about the size of a pebble. are those okay? also he lives alone. do the normally live in a group or "pack"? well i coud really use some help here thanks!