if you are intent about adding this one thing that i know with cichlids and more aggressive fish like triiger eel ... is that if you change the rock around in the tank it is new teritorry for both fish and this might help a bit but i have also heard that the four line wrasse is less aggressive that the six line and i agree with the prievious post that 6 line wrasse can be very aggressive against new fish
man i cant spell
let me know how it works out??!!
hop i waas helpfull