I am wanting to add a sea urchin to my 15 gallon tank. My tank CUC is currently one trochus snail and one blue leg hermit. The tank is 3 months old and has algae all over the rocks. My LFS has tiny urchins. I am planning on upgrading to a much bigger tank (100-150) over the next year. Would it be possible to add a sea urchin to the tank as a final member of CUC. Fish life is currently one clown fish.