We keep a lot of fish in our hard, pH = 7.8 water: a variety of tetras, angels, rasboras and of course, african cichlids. Stability of water parameters seems to be more essential than matching identically the 'native' waters. Also, a 30 gallon is too small for most Malawi cichlids. For example, I'd disagree with the above recommendation regarding zebras. They are not appropriate for such a small tank, IMO, unless they're small juveniles. Yellow labs may be OK, though, in a group of 4-6. Add a trio of a small catfish (e.g., Synodontis petricola) and you'd have a nice tank.
HTH,
Jim