PH swings could be something... but, if this was a water quality issue, wouldn't the juvie arrowana and pbass be worse off? Those two fish are not known for their hardiness as juvies.
I get asking about the water, most of the time it is the water. Insisting that it is the water after dude tests it is odd, unless you can say what the cat fish has, and why it has it. Insisting for actual numbers isn't odd but, why just go into every sick fish thread and shout "It's your water you dummy!"?