Only two of fish are fighting.....help

The tang in your picture is a Sohal Tang. THEY ARE VERY AGGRESSIVE. Probably the most aggressive of the tangs. You probably will not be able to add any other tangs as long as the Sohal is in there. In order to have success with Sohal's and other tangs, you really have to make the Sohal the last addition. Blue Hippo Tangs are very, very docile and really can't handle harassment. Turn the lights off and rearrange your rock work and bump up feedings, this might help a little. Don't move the rock where the Hippo is, it needs to feel safe right now.

Can you catch the Sohal and put it in a QT for a "time out" to allow the Hippo to acclimate? If not, the hippo will likely die.

you could try using a mirror i haven't heard success nor failure with this, but its worth a try the idea is that you put a mirror in the tank for aggressive fish to fight with wile the other gets used to his new home. it could work. :) good luck.

+1 BTLD's words...

If you can remove the sohal to a QT then after the hippo comes out re-arrange your rock a bit ,,, keep the sohal in the QT for about a week... if you can go longer then do that,,, then after he is added back have a day or 2 of dark or at most actinics....