Only One Crab Left Standing

After four days, I am sad to report only one crab left alive.  The shrimps, hermit crabs and fishes all died and the water smells terrible.  I fed the large hermit crab to the arowana.  It was still moving slightly and was eaten up immediately.  However, the shrimps sank to the bottom uneaten.  I have no idea why.  I need to figure out why and then try again.  Maybe due to lack of food, maybe insufficient water, maybe the sea anemone died poisoning the water and killing the rest.  The ecosystem is so fragile.  There is much to learn.