There are at least two great reasons for adding aquarium crabs to your tank. Crabs help to maintain water quality and they are fascinating to watch. Crabs are scavengers; they eat dead and decaying organic matter including dyeing plants. When you spill too much fish feed into your aquarium the crabs will help you out by eating the excess. An additional benefit is the incredible color crabs can add like the Red Apple Crab or the Purple Vampire Crab. They are also fascinating creatures to watch as they move about your tank foraging.