WHen I got this tank I was so worried about getting the water right. Now with all that behind me, I had 5 tetras. One got humpback and severe trouble with balance. It died. That was 3 wks ago. Now another tetra is the same way. I read something about tetra disease? How long do tetras live? All the others are ok for now. I watch my water like a hawk its always in range Please help.