Nitrogen Cycle

What is the Nitrogen Cycle?

The nitrogen is the cycle of nutrients in an aquarium. It takes ammonia which is toxic and breaks it down into less harmful chemicals to keep your fish healthy.

How does it work?

The Nitrogen cycle starts with fish waste and fish food. Uneaten food and fish waste decay into ammonia which is an extremely toxic chemical that causes respiratory issues in live animals. Thankfully there are bacteria in your tank that process it for you.

1st Step, Ammonia to Nitrite. Nitrosomonas bacteria consume this ammonia(NH3) and use it for energy, they break off the hydrogen atoms and replace them with oxygen atoms converting it into Nitrate(NO2) another toxic chemical.

2nd Step, Nitrite to Nitrate. Nitrobacter bacteria consume this toxic nitrite and attach another oxygen atom to it converting it into nitrate(NO3). Nitrate is much less toxic, and acts more as a fertilizer to plants and algae, too much can become toxic or lead to algae blooms so it must still be removed.

3rd Step, Removal of Nitrate. Nitrate is removed during water changes, and is eaten up by plants and algae. With and adequate amount of plants or water changes the nitrate level should not be a problem, however too much nitrate will cause algae to build up, and can eventually become toxic to fish.

Important Levels

We recommend all new fish keepers purchase a reliable water testing kit that can test for ammonia, nitrite, and nitrate, so they can track these levels with certainty until they become familiar enough with aquarium maintenance to notice issues visually. A fully cycled aquarium should be able to cycle 2ppm ammonia completely into nitrate within 24 hours.

Ammonia. Ammonia(NH3) should always be at 0.0ppm in a cycled tank, any level over that is toxic and cause for immediate concern. If you get a reading over this you should immediately do a large water change, add an ammonia detoxifying agent, like Seachem Prime, and then dose the tank with live bacteria. Detectable ammonia means either your tank is not properly cycled, or the cycle has crashed for some reason.

Nitrite. Nitrite(NO2) should always be at 0.0ppm in a fully cycled tank, any level above 0 causes severe respiratory distress in fish and other livestock. If you get a reading above 0 that means that your cycle has not fully completed and you should immediately preform a large water change and add live bacteria. Detectable nitrite means your tank is properly processing ammonia but is not fully cycled.

Nitrate. Nitrate(NO3) should be above 0 unless the tank is heavily planted or still cycling. Ideal levels are 5ppm to 20ppm. As you approach 40ppm you can start having algae blooms, and dirtiness building up in the tank, this level means you should do a water change, about half the tank volume should suffice, keep in mind that algae consumes nitrate making it undetectable, so lots of algae with a low nitrate value doesn't mean it isn't being produced, it just means its being eaten up. Levels near 80ppm start causing stress in the fish with levels above 100ppm becoming lethal depending on exact conditions, these numbers will be lower in more sensitive fish like discus, and higher in hardier fish like goldfish. Generally a very high number for nitrate, even if its not actively harming the fish means the tank is being neglected, and can indicate that other issues may be present such as the build up of harmful bacteria.

If you have any other questions about the nitrogen cycle or a problem your having with your tank, feel free to reach out via email or phone and we will help as best we can.