I just bought two fiddler crabs and in a matter of hours they picked the substrate and all my decorations clean of any algae or detritus. If you can house them, they are the best cleaner for any brackish tank.
I can't tell whether my other crab is a girl or a red claw crab. Oh yeah and I can't find it either, I've got so many hiding spots for them. I caught one of the males getting out so I put a barrier around the area so they can come out of the water when they want too.
they like to hide and get out! i'll post some pics of what i did to prevent her from getting out. its easy to tell if it a fiddler, one claw is bigger then the other, a whole lot bigger. heres a pic of my crab
I know both the males are in the tank but I can't find the female at all. She was hiding in one of my mangrove roots for a few hours after I got them and now she's gone. I checked around the area the smaller male climbed out and I can't find her.
I have RCC. I think they are really interesting and fun to watch. As long as the do not scurry away when they see you. Here's some pic's and info I wrote about the RCC. http://www.geocities.com/elgecko1989/crab.html