A large buildup of nitrates can cause the fish to get stressed, and if high enough, can kill them.
Nitrates are tolerable to fish and shrimp in low amounts. A large buildup of nitrates can cause the fish to get stressed, and if high enough, can kill them. The reason we do water changes is to remove some of the nitrates out of the aquarium. For example, if your aquarium reaches 40ppm of nitrates, you can do a 50% water change to get it down to 20ppm. By doing this, you’re replacing half of the “dirty” water with clean water.