Aquarium Nitrogen Cycle (The Complete How-To Guide)

Nitrogen Cycle In Aquarium

Have you ever wondered why experienced aquarists, after buying a new aquarium, leave it for a few weeks with only decaying dead shrimp or fish food and not a single live fish swimming around? Most likely, they’re probably waiting for their tank to cycle so it would be safe enough for the fish, shrimp, and other pets to live in. This is the single most important factor in the aquarium hobby and it cannot be ignored! You must learn the Nitrogen Cycle if you want to keep tropical fish. Your aquarium must cycle before you can house fish, if your tank doesn’t go through the Nitrogen Cycle your fish will die. NOT GOOD!

What Exactly Is The Nitrogen Cycle?

Nitrogen Cycle In Aquarium

Fish, shrimp, snails, and other pets you add to your tank all give off some kind of waste. This waste turns into ammonia, which is highly toxic to any tank inhabitant except for plants and algae. Fortunately, there are beneficial bacteria that actually convert ammonia into a less toxic form—nitrite. In most cases, however, nitrite is still highly toxic and could still be fatal to fish and invertebrates.

Fortunately, another group of beneficial bacteria converts nitrite to nitrate, which is tolerated by fish and invertebrates in relatively large amounts compared to ammonia and nitrite. These bacteria take time to grow; therefore, new aquariums that are immediately stocked with fish often experience the “new tank syndrome,” which leads to quick fish and invertebrate deaths. The nitrogen cycle immediately starts when a source of ammonia is present, which we’ll talk about further when we discuss the process of cycling your tank.

The Best Way To Cycle Your Tank?

To date, there are two main ways of cycling your tank: traditional cycling and fishless cycling. The traditional method of cycling involves adding a fish to your tank, thereby jump starting the beneficial bacterial colonies that convert the dangerous waste produced by the fish into less toxic form. Unfortunately, this process often kills or permanently damages the newly added fish due to exposure to toxic ammonia.

(WE RECOMMEND) The fishless method of cycling which is considered the faster and is definitely the more humane way of cycling a tank, simply because you’re not sacrificing a pet in the process. You’d simply need a pure ammonia source or even decaying matter to quickly jump start the beneficial bacterial colonies.

How To Do A Fishless Cycle

In order to do a fishless cycle, you can get a bottle of pure ammonia (Make sure that it’s 100% ammonia so you don’t get surfactants, perfumes, dyes, and other bad stuff aside from ammonia in your tank.). You can also use frozen grocery store shrimp or fish food locked inside a mesh bag since they also break down into ammonia when they start to decay. However, the pure ammonia approach will be much easier to control and will not contain fungus and other bad stuff that decaying matter could bring.

Here are the step-by-step instructions to help you do a fishless cycle:

1. Set up your aquarium – Fill it up with water and set-up your filters, rocks, substrate, plants, etc.

2. Add a dechlorinator to your aquarium – Chlorine kills bacteria, including the ones we’re trying to help grow colonies in the tank.

3. Keep the temperature stable (77°F-86°F) – The beneficial bacterial colonies grow quickly in this range, so keep it stable.

4. Leave the lights off if you don’t have plants – Plants love the high ammonia conditions of your tank, but so do algae. If you don’t have plants to absorb some of the ammonia in your tank, make sure you have the lights off to prevent algae from quickly covering your tank.

5. Turn on your filters and aerators – Anything that agitates the water surface helps oxygenate your tank and therefore encourages the beneficial bacteria to grow.

6. Add your ammonia source – Add about 4 ppm of ammonia (You’ll need an ammonia test kit for this.).

7. Find stuff from an old aquarium and add them to your new aquarium – From rocks to tacky aquarium decorations, beneficial bacteria colonies aren’t picky. Find stuff from an established tank to help seed beneficial bacterial colonies into your tank and help it cycle faster.

8. Wait and see – Keep checking your ammonia every few days; it’ll eventually start to drop. When it goes down to 1 ppm, dose it back to 4 ppm so as not to starve the beneficial bacteria. Do this about 1-2 more times, and then start testing for nitrite. Keep dosing ammonia to push ammonia levels back to 4 ppm, and keep an eye on nitrite levels. If the nitrite levels start to fall, then you’re on your way to the end of the cycle!

9. Water change – After a while, nitrites should drop down to zero. Nitrates should be really high at this point. You’ll want to remove about half of your tank water to remove a lot of nitrates.

10. Add fish! – When both ammonia and nitrites are zero, you can finally add fish as long as your nitrates stay at an acceptable level (For marine tanks, that’s about 0-20 ppm. For freshwater tanks, that’s about 10 ppm-40 ppm.). If the nitrates are too high, do a 50% water change. Remember never to do a 100% water change, as this may cause the nitrogen cycle to start all over again!

Nutrafin Mini Master Kit
Click Here To Purchase The Nutrafin Test Kit From Amazon

That’s it! After days or weeks of waiting, your aquarium is finally ready for its first fish! Cycling typically takes about a month to complete, possibly faster with the addition of stuff from established tanks.

Remember to stock slowly to give the beneficial bacterial colonies enough time to grow and adapt to the increased bioload. Test and change your water regularly and you should have a thriving tank in no time. (WE HIGHLY RECOMMEND) the Nutrafin Mini Master test kit to monitor your water parameters for its cost and its accuracy.


Previous articleThe Dwarf Gourami Care Guide (Trichogaster lalius)
Next articleChoosing Aquarium Plants
The team at Fishkeeping Advice work hard to bring you the most useful aquarium information and tropical fish care guides. Have an idea for an article? Let us know by sending us a message on Facebook