Some schooling fish can help make it feel more secure. I had good luck with tiger barbs till my demsey hit the 4" mark. Giant danios are pretty quick and big enough to not get eaten.I use silver dollars as target fish in one of my systems, but they get big so I wouldn't recommend them for a 4' tank.Tetras can work too. Pretty much anything that can't get eaten.....if you know a bigger tank is in the future, you could add some small cichlids