High DKH should not kill fish.
I am guessing this is ammonia or low Oxygen.. Things going higher up in the tank is because there is more oxygen higher up.
Not only that fish are breathing heavy... that is another sign of low oxygen or a sign of ammonia.
I would bet oxygen is dropping at night or it is ammonia.
I do not trust test kits so I always use two because I have had bad ones especially Salifert.
Another thing is PH could be dropping low at night but I doubt it would kill fish..
I am guessing this is ammonia or low Oxygen.. Things going higher up in the tank is because there is more oxygen higher up.
Not only that fish are breathing heavy... that is another sign of low oxygen or a sign of ammonia.
I would bet oxygen is dropping at night or it is ammonia.
I do not trust test kits so I always use two because I have had bad ones especially Salifert.
Another thing is PH could be dropping low at night but I doubt it would kill fish..