I've read before that a dose of 10ppm of nitrate can kill fish. Not that 10ppm is bad for fish, but adding it all at once has the possibility of killing fish. Supposedly, it's the sudden change.
I haven't personally tested it, but if you have fish dying, it might be worth adding something like 7.5ppm twice daily, or even cutting back on the dosing (if you have 40ppm). |