Make sure youR Groper is smaller than the tusk. I had a large tusk, 5" Australian, awsome teath, go in with my Groper 6". Who by the way tried to eat a mappa puffer twice his size, Well the puffer became 10 times his size, Well of point. But the groper is a nipper. He will creep up so slow, throught the rocks and take a bite, and off like a bolt of thunder to his home. I put the tank in 24 hour darkness moved rock and when we turned the lights on, war broke out again. I pulled the tusk And back he went. I must have mised a big battle as the tusk died 2 day after at the store.
So, IMO the tusk is more docile and will not grow as fast, so if you can not spend $$ on the big tusk best to forget about it or get it first, let it grow and then try the groper. The Coral Hind and the blue line act the same, so swaping out is not a good idea. and the panther will grow 8-12" a year untill it needs a huge tank.