well that tetra died on saturday,today another tetra was showing the same signs,i decided just to remove it and kill it humanely by throwing it hard against the concrete slabs,what i didn't expect was it just exploded as soon as it hit the slab,having used this method before,this never happened the last time,i think it was probably because it was so bloated,even looking inside the fish after it was dead,i could see no signs of anything!