Any Luck Keeping Red Devil With Other South Americans???

i have four very small south american cichlids, all between 1 and 1.5 inches. they are a gold saum, a jack dempsey, a convict, and a fish im thinking i may have stupidly bought not knowing what it is.... to find out its a red devil, or i am 99% sure anyways after looking at pictures online. i say stupidly because after researching this fish, basically every site ive read says that this is an extreamly aggresive fish once it starts to grow up. from my previous research ive already read that my other fish are no slouches, but from what im reading this red devil is supposed to be one bad mother. i basically just dont want to have him kill my other fish. they are in a planted 4ft. tank with a whisper EX up to 70gallon filter, there is quite a bit of hiding places for them (plants, log. rocks) and the most ive seen so far is just a little bit of chasing each other. i am aware that i will need a larger tank eventually so that i have two tanks (another 4ft or larger). but i guess my question is from all of your personal experiences with these specific fish, should i worry about this red devil killing my fish? what can i do to prevent this from happening? should i re-aranging they're environment often? what are recomended tank i will eventually need? just any info. i need to know about these specific fish i would greatly appreciate, thanks for any help

 

yea i had to remove the devil from my tank, it was about 2 - 2.5 inches and i kept doing the same thing to my jack dempsey, gold saum, and convict.... even was nipping at the pleco. so i moved it to its own tank.