compatibility jewel/johanni

I have a jewel and an electric blue johanni, both about 2 inches long,
living together and the jewel gets beat up once in a while but overall they
have survived together for a couple of months.

Recently I bought 2 more jewel cichlids about 1.5 inches long and the
electric blue was furious and would not rest until they were killed, so I
took out the new jewels and put them in an emergency tank, they are
recovered now.

So, are these two species very incompatible? What are good friends for my
electric blue and should I just have a tank dedicated to the jewel cichlids
given that they seem to be weaklings or can they also have friends of other
species?

Thanks for any advice on this. Sleddog.