I have a 29gal tank that houses 7 gold barbs, 6 panda corys, 3 bristle nose plecos. If like to add something else. ... either a single fish or small school. Problem is gold barbs are fairly aggressive. I've had guppies, platys, and a gourami which all died. The current fish have been around 6 months plus. Any suggestions or do I just leave as is?