Hola!
You could use either one. "Tu" is informal and "ud" is formal.
Cuando ves (ud. ve) ocho o mas horas de television diariamente tu (su) necesidad de ver la television parece ser incontrolable. Sufres (Ud. sufre) de la adiccion de la television.
It's even better to say "uno".
For example, "Cuando uno ve ocho o mas horas de television diriamente su necesidad de ver la television parece ser incontrable. Uno sufre de la adiccion de la television.=When one watches eight or more hours of T.V. daily one's necessity to wath T.V. seems uncontrolable. One suffers from T.V. addiction.
I hope I helped you-
Saludos