Please please please don't get jewel cichlids unless you are REALLY planning on breeding them. Otherwise it is utterly pointless.
They are best suited to large cichlid tanks, maybe with sevs or oscars.
Just remember, shops will market certain random cichlids as "jewel" cichlids because they havent got a clue what they are going on about, thoroughly research the particular cichlid you have seen.
Oh, and 20G long is NOT suitable for them.
If you want to breed a cichlid, rams or kribs would breed in that size tank, but tbh I would stick to your rams, danios and other small community fish.
Ben