Slight update on the Tilapia. I guess while in the eggs they could care less about the nitrate...

Because of their relatively impermeable chorion, the hatchability of tilapia eggs is largely unaffected by unionized ammonia (WOW! 101 PPM UNIONIZED) and nitrate.

REFERENCE
Rana, K.J., 1988. Reproductive biology and hatchery rearing oftilapia eggs and fry.