Understanding the Nitrogen Cycle: A Guide for Aquariums

What is the Nitrogen Cycle?

The nitrogen cycle is the backbone of every healthy aquarium. It’s a natural process that breaks down fish poop, uneaten food, and dead plants (called ammonia) into less harmful chemicals, keeping your water safe for your fish. When fish poo and organic matter break down, they produce a chemical called ammonia. This is a toxic substance that can be deadly to fish, shrimp, and snails. Butttt don’t worry! The hero in this story is actually an unlikely one, bacteria. Beneficial bacteria in your fish tank converts this ammonia into a new chemical called nitrite, which unfortunately is still harmful, BUT less harmful, so that’s a plus! But that bacteria isn’t done yet! A second type of bacteria is born to consume the nitrite, turning now into nitrate (notice there’s an A in this word), which is much much less toxic to aquatic life and can be managed with regular water changes or adding lots of plants.

This process is called the Nitrogen Cycle. It’s a vital part in the success of any fish tank, and unfortunately, it’s often missed by many new hobbyists. I get it, the excitement takes over, and the last thing people want to do is sit with a brand new, empty fish tank. But if you’re interested in healthy, stress free fish — Read on!

Why is the Nitrogen Cycle Important in Aquariums?

The nitrogen cycle is vital because without it, the toxic chemicals in the water would build up so fast, your fish, shrimp, snails, and plants would all be rapidly poisoned and killed. Think about it, all fish poop, right? And we love to feed fish, because it’s fun and they’re cute, right? Andddd we sometimes give them a little extra, because they look SO hungry! But all of that shocks a new tank. It immediately turns the water into a concoction that is full of nasty things. Like a soup you’d never want to eat. Poor fish, they’re living in that! This is why you want to cycle your tank BEFORE you buy your fish.

What are the Stages of the Nitrogen Cycle?

The nitrogen cycle has three main stages: 1. ammonia, 2. nitrite, and 3. nitrate. If your tank is truly cycled, you will usually only ever have #3, nitrates.

Ammonia Stage

Everything starts with ammonia, produced by fish poo, food, and decaying plants. Ammonia is very, very toxic to fish, but the good news is that bacteria called “Nitrosomonas,” step in to convert ammonia into nitrite. Thus reducing the toxicity. This process isn’t instant, it can take hours and sometimes days depending on how mature the tank is, so it’s essential to monitor ammonia levels closely, especially in new tanks with fish.

Nitrite Stage

Once ammonia is converted, you’re in the nitrite stage. YEAH! Nitrite is still harmful to your fish. Awe… It will cause stress and even gill damage if it gets too high. But, another set of bacteria, “Nitrobacter,” gobbles up the nitrite, converting it to nitrate. And just like our arch nemesis ammonia, you’ll need to keep an eye on nitrite levels to ensure they don’t spike either.

Nitrate Stage

Finally, nitrite is turned into nitrate… Phew. Nitrate is FAR less harmful, but can still be a problem if it builds up too much. High nitrate levels can lead to stressed fish, unwanted algae growth, and if it’s left totally to it’s own devices, fish poisoning. However, the remedy is really easy — New water and plants! Regular water changes are your best defense against nitrate. But the good news is, is that this is the last stage in the cycle. If you’re starting a new tank, you’ll it’s ready for fish when you test the water and find it has 0ppm ammonia, 0ppm nitrite, and any amount of nitrates.

If you want more information on testing your water, check out this article on How to Test Aquarium Water Parameters.

How to Establish the Nitrogen Cycle in Your Tank?

It’s already been said, getting the nitrogen cycle going prior to putting in fish is the ideal way to go — For the fish, we get it’s not so much for you. Here’s how we do it:

1. 1. Set Up the Tank: Start by adding water, water conditioner, substrate, decorations, and your equipment like the filter and heater. If you’re brand new, here’s a guide to setting up your new tank.
2. 2. Add a Source of Ammonia: To kickstart the cycle, add some fish food, or a small amount of ammonia. This is a great product for cycling a tank. This provides the ammonia needed for the bacteria to start growing.
3. 3. Introduce Beneficial Bacteria: Speed up the process by adding a bacteria supplement or seeding your tank with media from an established aquarium. “Seeding” means squeezing out old filter media into a new tank, thus transferring the established bacteria.
4. 4. Monitor Water Parameters: Every few days, test for ammonia, nitrite, and nitrate levels. This will help you track how the cycle is progressing. Here is what I use to test: API Master Kit.
5. 4. Repeat: Start slow! Don’t add too much ammonia or fish food to start. Once you add a little, wait a few days, then add a little more, then a little more. Slowly build up the amount you add. Only do this a couple of times.
6. 6. Be Patient: To completely cycle your tank can typically take 4-6 weeks to complete. I know it’s hard, but hold off on adding fish until ammonia and nitrite levels are at zero. Trust me, it’s worth it.

If you want a more detailed guide on cycling your tank, check out our article, “Fastest Way to Cycle a Fish Tank.”

How to Speed Up the Nitrogen Cycle?

This process is grueling. When all you want to do is have a boat load of happy fish, waiting for the nitrogen cycle to complete can feel like forever. That being said, there are a few ways to speed it up:

• Use a Bacteria Supplement: Adding beneficial bacteria directly to your tank can jumpstart the cycle. Products like Seachem Stability or Microbe-Lift Special Blendare great for this. I use both.
• Seed Your Tank: If you have another tank, or a friend with a well established tank, use media from it to give your cycle a significant boost. BUT beware. If you’re using a friends media, keep in mind that with the good, comes the bad. They could have algae, snails, or diseases in their tank. Some of that will also transfer with the bacteria.
• Increase Oxygen Levels: Boost the bacterial growth by increasing aeration in your tank. Use an air pump with an air stone, or two!
• Maintain Stable Temperature: Make sure you have a good heater, and warm the water up to about 78-82 degrees. Keeping the water temperature consistent and high supports faster bacterial growth.

Follow these strategies, and they can help you get the nitrogen cycle going faster, which gets your tank ready for fish sooner!

Common Issues with the Nitrogen Cycle

Even with the best efforts and all the research, the nitrogen cycle can present some challenges too. Here are common issues I’ve faced, and how you can deal with them:

Ammonia and Nitrite Spikes

Spikes in ammonia or nitrite can seriously stress your fish, if you have fish in there. If you notice high levels, perform partial water changes (remove 20% of the water, and add new, conditioned water back in) to dilute the concentration. Bear in mind too, if add too much ammonia or fish food, you can cause an outbreak of algae or halt the cycle completely.

Slow Cycle Progress

Sometimes the cycle takes longer than expected, this can be for a lot of reasons. Make sure your tank conditions are ideal: steady temperature, good aeration, and add a bacteria supplement. If it’s still taking time, less might be more. Often times, we can get over zealous and add too much ammonia mix or fish food. This can make the water too toxic for bacteria to form. So, start slowly and build up.

Algae Growth

If you’re really cranking through this process, you might cause high nitrate levels. This can be fuel on the fire for algae growth. You’ll likely need to do water changes and maybe adjust the light timing to help keep algae under control.

Conclusion

We hope this article helped you learn a little more about the nitrogen cycle. It can sound a little intimidating at first, but I hope it was able to presented in an understandable way. If you follow our steps we laid out, we know you’ll be successful and that your fish will be all the happier for it. If you have questions or concerns, post a comment below or contact us directly.

For more tips and advice on aquarium care, be sure to visit my blog.