Yesterday I did a 25% water change of my 80 Gallon tank with 12 African Cichlids, a Senegal Bichir, A Clownknife, a Crawdad, and a pleco in it. And when I woke up this morning one of my African Cichlids was dead and the fish are all going up to the top for air WAYY long then usual... Is there something wrong? Thanks!