I noticed this morning that one of my cories is completely missing his back tail and fin. It nearly looks like he is chopped in half. The end looks kind of feathery like it's growing back already. He is breathing really fast and stressed out but he was also eating and swimming around. I turned off the lights to let him rest and brought some stress coat, I put 40 mls for my 100 L is that too much? It says add 5 mls for every 38 L and double the amount for damaged fins