Hey so i just reset up my old tank, I was waiting for some gold fish to pass on and after they did I did a complete overhaul on the tank, cleaned it completely and changed all the water. Then I set it back up and waited for the biological cycle or whatever to kick in. After the water was cloudy and then became clear, I added 5 fancy tail male guppies. Everything went fine for a few days but then one's tail became shredded and it soon died. Then another day passed and anothers tail was shredded. And now, a seemingly normal guppy is starting to float belly up, but the other fish in my tank seem to be doing fine. I have one live plant in the tank, and the temperature is a steady 84-85F. I check ammonia and nitrates and stuff, and the only thing off was that my water was hard, but thats it. What can I do to prevent my fish from dying?