I have had 5 total fish die in the last week but have no clue why, the ammonia is 0 the nitrite is 0 and nitrates are at a healthy level (just water change on Saturday) i have a 55 gallon with 4 angle fish 1 pleco 1 catfish 5 black skirt tetras and 3 gold fish currently. I added some API general desease packets hoping that will help, but other than that i have exhausted any other options and i am at my last wit. Have done 50% water changes concurrently for months so i cant see that being the issue considering the bioload in my tank is quiet heavy. My tank is fully cycled and i feed once a day. The temp is at 78-80 degrees F