Here's a care sheet:
http://www.austinsturtlepage.com/Car...ear_slider.htm
The turtle pellets are considered to be a sufficient vitamin supplement. Be sure to buy a good-quality brand, such as Mazuri or ReptoMin. Provide veggies daily (Romaine/Red-Leaf/Green-Leaf lettuces, endive, escarole, mustard greens, dandelion greens). Aquatic plants are a good addition to the diet (they like anacharis a lot). You can put guppies in the tank, they'll eat them, and get some exercise and enrichment in the process. Don't use feeder goldfish ver often; they're too fatty for frequent feedings. Your turlte will get very large, if a male, he'll get to 9 inches SCL, and a female could get to 12 inches SCL. Figure on 10 gallons of tank space for every inch of turtle. This does mean that a female will eventually need a 120 gallon tank.