I don't think that's too many. I had more than that in my 90 -- I had two different fromias, a blue linckia, an orange/red linkia, a serpent and a brittle star. As long as they are getting enough to eat, they are fine together. As Sarah said, linckias are very difficult to keep alive. For some reason, they are just tough critters to keep; and I'm not sure people know why -- it is thought that they starve to death. Be careful of your sand sifting star, though. Those guys starve to death a lot too, especially in newer tanks. They just run out of food.