A few weeks ago I lost many of my female guppies following a sudden pH drop. This left me with 4 males and 2 females. I fixed the water problem but decided not to add more fish for a few weeks to allow the survivers time to recover. Yesterday I added 6 new females to restore the Ballance of males to females. This morning one of my males had half his tail missing and I saw both the other males and the new females attacking him. I moved him to a hospital tank but he soon died. I have never had a guppy attacking another guppy before. Now my remaining males that usually dart around the tank are hiding in the corners. I have checked the water and nothing is wrong with it. The new fish have been quarantined for 3 weeks. Has anyone any ideas?