I bought a new male Fancy tailed guppie yesterday. this morning his tail is half shredded. I have in with him in my tank, 2 female guppies, 2 corys, 2tetras, 2 neons, 1 large algie eater. My tank tests all fine, the pet store checked evrything too. If you know what causes this please tell me,this is not the first time this has happened, but it has not hapeened for some time now.