I started out with 6 hermit crabs and now I have 4. I don't get why they died. My nitrates are usually below 20 ppm. There's quite a bit of algae and every once in a while I put a piece of shrimp in for them to munch on. I don't have a whole lot of shells but there seems to be enough considering how few there are. I had 5 red legs and 1 blue leg. The blue leg changed shells twice before it went missing (I found the shell it was in), but I haven't noticed any of the red legs change shells. I haven't lost any snails and my two starfish seem fine. Any ideas?