I have a new 29 gal tank witch has just finished cycling. I have had 3 green cromids and 3 hermit crabs, all was well had a green hair algae problem but the fish store gave me some stuff to fix it and it seems to be working. Had the water tested and all was fine so I put in 1 polyp and 1 cool red worm thing that terns white when it is scared. I have bin putting in live rock slowly now have about 36 lbs. This morning when I woke up 2 of the hrmet crabs were out of there shell and one was dead. Have I done something wrong, can I fix it or is this normal