First sign of anything wrong..... waterchange, Then repeat every couple days till you know what caused the problem....
I use rock salt or kosher salt/pickling salt 0.03% Works for just about anything arowana related.
My arowana is all better now. I bumped up the heat to 85 degrees and added about 1/2 dose aqaurium salt. Reduced feedings to once a day and completed water changes ever 3 days until he cured up.