They're not called earth eaters for nothing, lol. A small smooth substrate will let them sift through it. Don't plan on rooted plants, they dig!! Actually you "may" be able to have rooted plants if you place larger rocks around the plant bases. But you can have plants like ferns & anubias attached to wood or rocks.
If you have a M & F pair you won't be able to keep much else with them. They will eventually breed. That can be cool the first couple times...& then they'll breed every month! It can be hard to sell/give away cichlid fry... especially at the size you'll want to remove them. That's not the size most LFS want or club buyers either.
Things will be different if you only have a single geo, male for prettiness, female for smaller size. Larger tetras might work, nothing bite size to a 5-8 inch fish. Geos aren't very aggressive but, like any fish, if it fits (or part of it fits) in it's mouth, it may well be food. We kept giant danios with midsize cichlids, but they jump!
