Saltwater pets are much easier to cope with high nitrite levels compared to freshwater ones. Accordingly, the recommended nitrate levels in saltwater aquarium (fish-only aquarium) are between 10 and 40 PPM (parts per million). On the other hand, when we talk about safe nitrate levels in a saltwater aquarium that contain invertebrates and corals, they are 2 PPM.
Aquariums containing invertebrates must pay special attention to nitrate levels because these animals are generally delicate and therefore sensitive to contaminants. Some specimens could tolerate levels above 5 PPM, but for most anemones and corals such levels would be too high and potentially lethal.