Great advice here.It seems that the repeated theme with these turtles is they are opportunistic omnivores, but are mainly herbivorous. So IMO feeding a quality pellet mix that is herbivorous based (aquatic based plant matter), will typically be far better than the lower quality/cost terrestrial based ingredients utilized in most pellets specifically designed for turtles. Also, quality pellets that are designed for fish, such as NLS and Northfin, are supplemented with vitamin B3, so IMO no need for buying a specialty UVB bulb when a quality diet is being fed.
Back when I kept these guys I also found that adding crushed coral to the system improved any skin/shell issues I was seeing. They like a slightly basic water chemistry.