from what i seen cause the 1 in my 24 an one of the 1's in my 20 i originally bought together an had in the 24 sounds like you got 2 males. when i had mine both in the 24 when were just 2 of them one never got to eat cause the dominant one beat him down so bad he hid in the rock work even then he get harassed so i split them into 2 tanks did more research did find articles saying they do like groups but odd numbered groups to distribute the agression so the weakest one don't get killed thats why i was thinking 55 be perfect to attempt this. read articles where they suggest getting 6 to increase chance of getting a female so i thought get 6 with what i already have an possibly a pair already bonded though kind of leary of that since this last pair i got was supposed to be bonded an now not 100 % percent sure that the pair was a male/female pair cause my estab;ished male is staying by himself today. so the 1 i thought could have been a female might also be male so thinking trying a small army in 55 an hope that gets atleast 1-2 hopefully more females an be able to get them to where if they do fight wont be deadly till i get them paired off an mved to 20-30 gallon tanks an put just a pair in each tank with a pair of clowns in each also. with the 55 hoping to put some seahorses in also since bangaii's are usually pretty seditary.
Seems today 1 bangaii was dead an it was one of the new ones seems the lfs
sold a pair that were really 2 males as the last 1 is being chased so will be putting him in the 55 gallon as of tonight. so now got 3 males no females.