I have a 30 gallon tank up and running for about 5 months now, it is good shape with great water quality. I have a six line wrasse, saddleback clown, percula clown, and a lawnmower blenny. Also some hermits and snails. the fish all get along great. I had a sand sifter star, but it got killed in about 3 weeks. All anyone has told me is that it is probably some unwanted crabs or other pest from the live rock. What can i do to get rid of these pests? or is there another explanation?