And remember, West Africans (like the krib) have similar water requirements to New Worlds (CA/SA), like your ram and some CAs from the crater lakes can tolerate water similar to Malawi but not as hard as Tanganyika. Confused yet?
Basicly New Worlds are from North America (Central and South America mostly although many can now be found wild in Florida, Texas etc.) They prefer a pH around neutral and softer water temp in the upper seventies. But they are tough as nails and will take up to a high seven pH and cooler water (its just not preferred). The West African river species (the only ones you are ever likely to see are jewels and kribs) prefer similar conditions.
Old Worlds are generally from African Lakes Malawi and Tanganyika. I know nothing about them and couldn't tell a Hap from a Mbuna so I will leave someone else to give advice, but from what little I know Tangs prefer the most alkaline and hardest water.
Central American cichlids are, in general, a hundred times meaner than Africans and grow (in general again because there are species that negate this rule of thumb) much larger and need a huge territory and consequently tank.
South Americans (although there are some agressive species here too) are a little less outright mean than the CA but still territorial. There are also some docile species found here like your eartheaters and dwarves.
Always remember though when you see docile read it "won't gut tank mates and shred their fins in fifteen minutes flat". Other than that all I can say is google the fish and research it before you buy it otherwise you will learn the hard way with WWIII in your tank and lots of dead fish (thats how I learned before I found this forum).HTH
