The "net ionic" equation only shows the chemical species involved in the reaction, none of the spectator ions. So you disassociate all the ions in the reaction and only keep the ones that make the sold.
[tex] \\ Disassociate \\ Ba^{2+} + 2Cl^{-} + 2H^{+ } + ( SO_{4} )^{2-} --\ \textgreater \ Ba(SO_{4}) + 2H^{+} + 2Cl^{-} \\ \\ - Spectator..Ions \\ Ba^{2+} (aq) + ( SO_{4} )^{2-} (aq) --\ \textgreater \ Ba(SO_{4}) (s)[/tex]
