I have a 55 gallon tank with a 10 gallon sump underneath. There is approximately 4 inches of live sand on the bottom, 80 pounds of live rock, a protein skimmer, and a fluidized fliter in the sump. My problem is this; My son loves Sally lightfoot crabs so we have triied 4, at different times, with the longest lived one being about 2 months and the shortest lived being the most recent 3 days. The occupants of the tank are; 2 Percula Clowns, 1 Domino Damsel, 2 Brittle Starfish, 1 Arrow Crab, and 1 Cleaner shrimp. Does anyone have any ideas why these keep dieing? Everything else is doing fine.