I'm sorry angryc, but I do not recommend putting a green terror with an ebjd. Please do not do this, especially in a 55. That is just a good way to end up with dead fish. No, not if you do that many frequent water changes and have that good filtration you are not currently overstocked. Thanks for the additional information. Here are a few suggestions:
1. Texas Cichlid (Will get a bit big, but may work)
2. Kribensis (Yes, it is African but it has been known by American cichlid lovers to often fit right in)
3. Apistos/ Dward cichlids as I mentioned earlier
4. Normal or Gold Jack Dempsey
5. My personal favorite of these options, a Blue Acara (looks like a green terror, but fits perfectly in with your fish and stays a good size)
Good luck!