What Is Nitrate?

Nitrate, commonly confused with nitrite, is the last step in the nitrogen cycle of your fish tank. It is the least toxic of the bunch (ammonia, nitrite, and nitrate), but it can still be toxic – even if it is at high levels.

Nitrate, since it can’t be converted further, needs to be taken out of your aquarium via water changes or plants. Most fast-growing plants plants like hornwort, guppy grass, or water wisteria will gladly take up the excess. Conversely, dying plants release large amounts of nitrate and nitrites that they had “locked in” while growing, which can cause some serious issues in your aquarium. 

Ideally, a healthy tank will hover somewhere around 5 – 10 ppm for nitrate. Around 20 ppm you’ll likely see algae and health issues in your tank, and in excess of 50 ppm you’ll likely see some fatalities.

Nitrates, although less commonly than nitrites, can also come from fish food, plant fertilizers, or your tap water. Most commonly from your tap water, especially if you have a well. Most of the time if ammonia gets into your well, the bacteria in the surrounding spil will convert it to nitrite and then to nitrate. But, since nitrate can’t be further converted, it’ll come out of your tap.