[TheXman]

Actually, praecox rainbowfish are not a brackish species. They may survive in it because rainbowfish tend to be pretty resilient, but they will do much better (live longer, show better color, etc.) in freshwater. They will also do better in a larger tank, like tophat said, they are active and need some room to swim. Who told you that praecox were brackish fish? Someone must have gotten them confused with one of the blue eyes species. In any case, fiddler crabs and praecox aren't compatible, they have totally different water and tank set-up requirements. If you want to keep the crabs, you should get another (hopefully larger) tank to use as a freshwater set-up for the praecox, or take them back to the store you bought them at, or find someone to take them off your hands.

 

[TheXman]

You're making some assumptions here that are wrong. First of all, Ram cichlids actually do NOT tolerate brackish water very well at all. Ram cichlids are South American cichlids (like Discus) and just like discus, they like very soft, slightly acidic water, just the opposite of African cichlids, and a far cry from brackish. I don't know about kribs, but I do know that Praecox rainbows really are freshwater fish. They come from remote jungle streams in Papua New Guinea that are freshwater, not deltas or estuaries, or brackish lakes. They really aren't all that picky about hardness and are pretty resilient which is probably why they are doing well so far, but brackish is pushing it. Long term, they'll do much better in freshwater, but don't take my word for it, there are dozens of people who keep Praecox rainbows (including some of the most knowledgeable rainbowfish breeders in the US and Canada) on another site: http://bowheads.org/