Eartheaters (Geophagus, Satanoperca, Gymnogeophagus, etc.) come in many
sizes and temperaments. Would really need to know which eartheater you
are considering. But with all these fish, temperament and compatibility
vary among individuals. I would say your proposal stands a reasonable
chance of success, however. Personally, however, with your water
chemistry, I would go with apistogramma, Rams, etc. 55 gallon tanks are
odd shaped tanks, being so narrow. They are really better for small or
slow moving fish. Severums and some species of eartheaters will
eventually outgrow them.

I plan on getting Geophagus jurupari. I believe they generally have a good
disposition.

Yes. There is not much bottom area in a 55 gallon tank. There would not
be enough room for four pairs to set up territories.

I agree, I am going with 3 pairs.

I would like to thank you and NetMax for great input. It's people like you
that keep these groups alive.

Steve