Got a high reading for Nitrate levels today and changed out water about 1 third of a 30 gallon tank. Fire Gobys seem fine, but I lost my Arrow Crab. I don't know if it was the nitrate levels or the change of water or it just got old. I've had the crab for about 6 mohths. Grows fast, but not sure about it's life span People have them for about 1 year from what I can tell. When you get them at the store, how can you tell how old it is? I got it mainly to eat the marine worms. I have to get something. Any suggestions?