I woke up this morning finding one of my sens hardly being able to stay up straight and had lost a lot of his color. The tank is a 75 and is stocked with 2 sens, 1 delhezi, 1 bowfin, 1 guinien bichir, and 2 angels. The bichirs range in size from 7'' to 9''. There is never any aggression i haven't added anything new to the tank in months. Last night i did a weekly 50% wc and thats really the only thing that i could think stressed out my sen. I tested my water and everything came out good but the ph came out low at about 5.5. I dont know what would have caused him to die. I went out and got some stress zyme and when i got back he was upside down dead. im a little upset because he was the first bichir i got and Ive had him about 2 years. so if anyone has any idea what may have happend let me know what you think. Also he ate normal every night and i saw no signs of sickness last night before i went to bed.