What you need to know about Nitrate (NO3)

Where does it come from?

• Most nitrates come from the organic breakdown of nutrients from food.

• Tap water can be a source of nitrate.

• Algae such as Blue Green algae seem to raise nitrate levels if they aren’t removed regularly because they store massive amounts of it, so when they die or are eaten the nitrates are set back in to the environment.

• Some invertebrate foods may introduce nitrate.

• If you run ozone on the tank this can sometimes be a cause for high nitrate.

• Some salt mixes and fertilizers contain NO3.


What problems does high Nitrate cause?

• Algae blooms.

• Lowers pH and hardness.

• Causes corals to contract.

• Causes stress and respiratory problem with the fish.

• Lowers the fish’s immune system.

• Weaken fish’s body slime.

• Hamper the diffusing of oxygen across the gill lining.

• The effect nitrate has on coral varies from species to species.


What levels should it be?

• A reef aquarium should be maintained less than 1ppm.

• Above 5 ppm for a reef and 10 or 20ppm for a fish only tank is not acceptable.

• If you choose to have a nitrate level of between 1ppm to 10ppm, the corals may grow faster but remember that it will affect the pH, alkalinity and calcium level, so ensure that they are maintained.


What effect do water changes have on nitrate?

• In general water changes have a positive effect, lowering nitrate.

• If your tank level is low and the water used for water changes has a higher level, then it can create a negative effect and you may consider R.O water.


How do you lower Nitrate?

• Adding less food to the tank will help lower nitrate. Remember that the health of the fish is more important than a bit of nitrate so don’t starve them.

• The use of mechanical filtration or a protein skimmer will remove much of the organic matter that would have been broken down into nitrate.

• The establishment of anaerobic zones (in the middle of the live rock or in deep substrate) will carry out denitrification that can break down nitrate into gases.

• An aquarium with established live rock alone or plus live sand should be adequate with time to obtain little or no nitrate without an additional nitrifying filter.

• Minimizing pure nitrification e.g. bio balls can lower nitrate levels.

• The use of R.O water will aid nitrate reduction.

• There are resin and sponges available to lower nitrate.

• The use of activated carbon aids in nitrate reduction.

• Growths of algae will help to lower nitrate, especially an algae bed filter.

• The addition of grazing and scavenging creatures like fish and snails help to lower nitrate because they use some of the nitrogen in the algae and debris that they consume.

• There are various denitrification filters available.

• See the question ‘How do I lower my organic waste’ in the articles section of the Majestic Aquariums website.


Good luck & enjoy,

Paul Talbot