Very limited on what you can stick in 20 gal. These are great and beautiful fish but they have there down fails of who can go with who.
This is true. My krib is going to have to be moved in the not to distant future as he's beginning to bully the rams a little to much.
My advice for a 20g for cichlids is a small group of rams like 2-3. Give them plenty of hiding places etc and the best possible water conditions and they will thrive.
I've read rams can be a little sensitive to bad water. Blues being the most sensitive then golds and the bolivian butterfly the most hardy.
There's other dwarfs cichlids to choose from though, so look around.
ps. if you like the rams, the German blue ram is probably the most colourful.