I think your biggest problem is not having a qt
AND having so many fish (especially ones that get LARGE) in your tank... In your profile you have a 44 gallon, that is not very big for the Humma Humma, and even worse for the Niger... take it slow... get a qt
and put the new fish in there for 4 weeks... then add it. Also I would get some better choices of fish. RESEARCH!!!!! Get gobies, cardinalfish, clowns, and blennies, not these guys that will outgrow your tank in a matter of a year!