Dark color is dissatisfied with the performance of the water quality, black is its pressure line changes, the body of adrenaline secretion caused by too much general home raised submarine 70% will appear this situation did not see your tank of the overall equipment and water quality how dare not in vain to jump to conclusions, can only give you two aspects of the proposal: 1-added coarse salt, according to the weight of the water 2% of the amount of water with, don't use table salt, iodine will be iodine poisoning, the green pufferfish is the estuary! Fish, the origin of life in the waters is a certain salinity, fresh water is often a direct cause of its death 2 - hypoxia, submarines are prone to hypoxia, if you tank is small and no filtration system, then it is very easy to turn over the belly of the situation