biocube issue

So I set up a 14th biocube in July the tank has cycled and I have added some coral . The coral has been in for at least a month and a half (zoo and blue mushrooms ) and they have prospere. But when I have added fish they have lasted about 15 to 30 days thenow die . My nitrate amonia nitrite and pH are fine Sg is 1.027.



2 green chromis have died and one Clown (never were all Inight tank together )



Any advice would be nice going crazy over this:angry::angry: