woke up today , went out to my fish shed and bam my big checkboard (15-18cm)male discus is dead , he was part of a pair which were in a breeding tank, and yet he was fine the day before i.e swimming fin, breathing normal, no stress bars (temp is 84, p.h 6.6, and all other test came out 0) so can someone help me with what has happen because i have no idea