i've been reading a lot of stuff about GBRs being sensitive and stuff...in my personal experience they're not.
i've done the ff while the GBR was in my tank:
- replaced the white sand with river sand(turning my tank into the Mississippi)
- often forgetting to do water changes
(yeah, not exactly proud of it)
...yet my pair is still happily ticking along. Dunno if they're wild-caught or anything, but they're certainly not "sensitive".
My "dream fish" now is a pair of apistogramma agasizii's. i hesitate because i don't have any room anymore.
You can also look into African dwarfs. Interesting shell-dwellers too.