I've had some small, 3 medium and a large in my 12g tank for about 6 months. I dose dt's phytoplankton 1-2x a week and they seem to be doing well. I wouldnt keep them with agressive crabs. I use scarlets and blue leg and they seem to live in harmony. I also have peppermint, sexy dancer, and pederson shrimp and they're all fine together. A coco worm might be a better choice if you have a more agressive reef because the tube is calciferous.