Updated: Sep 27, 2020

A diagram showing the nitrogen cycle from fish waste to ammonia to nitrites to nitrates
The Nitrogen Cycle converts harmful ammonia produced by fish waste into harmful nitrite and then to harmless nitrates and must be done before any livestock is introduced to the aquarium.

Much to my wife’s chagrin, our garage has become filled with buckets and trash cans of water. I’m not talking about the trashcans that serve as my salt water mixing station. I’m talking about additional vats of water taking over our garage. But, I keep pleading, those holding tanks are necessary because I need to get my nitrogen cycle running outside of an aquarium.

Now I know what you are thinking: that makes no sense. For seasoned aquarists, it doesn’t make sense to run the cycle without the tank—the whole point is to get the tank established and ready for livestock. For those new to the hobby, it makes no sense because the concept of a nitrogen cycle is unfamiliar.

Let me start by explaining the nitrogen cycle and why it is important. Then I’ll explain why I am doing this in an unorthodox manner without a tank.


The thing to keep in mind is that an aquarium is a closed system. Fish are living animals that produce biological waste just as we do. While we can flush our waste down toilets into an elaborate sewer system, fish cannot. They are swimming in their own waste. This waste (along with decaying food and other dying microorganisms that inhabit the aquarium) eventually break down into ammonia.

Ammonia is bad. It is toxic to your livestock and will kill your fish. Established bacteria, however, will convert this toxic ammonia to nitrite (still harmful to your fish) and then to nitrate, which is not toxic to the fish and can be kept in check through routine water changes (which you will want to make as easy as possible). The trick is to have enough of that bacteria established in the tank to keep up with all the ammonia that the fish (and other animals) are producing.

The cycle of waste —> ammonia —> nitrite —> nitrate is known as the “nitrogen cycle,” the “biological cycle,” or simply “cycling your tank.” Before you put any livestock in your aquarium (clean up crew, fish, corals, invertebrates, etc.), you want your tank to have gone through the cycle proving that it has the necessary bacteria to detoxify the ammonia your livestock will produce.

If you add livestock before the tank is cycled, the livestock will be in the water the same that the toxic ammonia and nitrites are rising. If your fish survive that toxic pool, they will be super stressed and unhealthy on the backend. You should always cycle your tank without fish in it! (May of the products I recommend below claim you can add fish right away. Don’t do it! Fish may survive but they won’y be happy! I even cycled my 1 gallon betta tank before introducing a fish!)

The reason people want to believe in the fast cycle or the fish-in cycle is because cycling tanks a while. Every tank is different and there is no telling how long it will take. It can take 2 weeks or it can take 2 months. It will be finished when it is finished and there is no reason to rush it.


Under normal circumstances, cycling a tank is very simple. You simply set up the tank, add a bit of ammonia, add a bit of bacteria and . . . wait.

Let’s break that down. For a saltwater reef, you would buy some live sand (live because it contains the bacteria and microorganisms you are looking for), some rock and do your aquascape. (Pro tip: use dry rock rather than live rock—cheaper, lighter (cheaper shipping) and won’t come with nuisance pests and parasites that can otherwise find their way into your tank through live rock.). After you add water, put in some ammonia to get the cycle going. I use Dr. Tim’s Ammonia Chloride solution—4 drops per gallon. You’ll need to keep adding ammonia until your ammonia measures 2 parts per million. This can be easily measured with the API test kits. Another easy way to keep track of ammonia in your tank is the Seachem Ammonia Alert badge. I have one of these in each of my aquariums, although I use the test kits during the cycling stage.

Once your ammonia reaches 2 parts per million, it is time to start seeding it with bacteria. There are all sorts of products, like API Quickstart, Seachem Prime, and Dr. Tim’s One and Only. I have used them all and I like One and Only the best. As mentioned above, although many of these products claim you can simply add a minimal dosage and toss in fish right away, DO NOT DO THAT. Dose the bacteria every day until your tests show the complete cycle is finished, i.e. ammonia has gone down followed by a nitrite spike and a nitrate spike. When that cycle is complete, do a water change and you are good to slowly add livestock. Your tank is now seeded with beneficial bacteria—it is all over your rocks, sand and filter and will help break down the ammonia your livestock produced.

The process is the same for freshwater tanks, although you will not be using live sand or live rock. But you will cycle whatever gravel, decorations and filters you have running using the same method as above. We recently built the children's’ SpongeBob freshwater tank and it took almost a month to cycle following this method. This hobby did teach them patience, however!

Picture of freshwater aquarium with SpongeBob decorations
The boys' SpongeBob Tank


I am in the middle of a new aquarium build. I have an existing 14 gallon reef with a 7 gallon sump and an existing 10 gallon coral frag tank. I am building a 40 gallon predator reef tank. The current plan is to connect all three tanks. Each will drain into a single 55 gallon sump for filtration with a powerful pump that will push water up to each tank. This will benefit my system because it will add more total water volume, which means more stability. The separate tanks will also let me keep an array of livestock that I normally would not be able to keep together. I can keep small, docile reef fish in my 14 gallon with larger, majestic predators in my 40 gallon.

This build presents unique challenges, however. Once set up, the new 40 gallon display and 55 gallon sump are sure to go through a cycle. Since these will be plumbed into a single sump with the two smaller tanks, the smaller tanks are bound to suffer. I won’t be able to cycle a 40 gallon and 55 gallon sump and then move nearly 1,000 pounds to the common stand and plumb it all together, take each system offline while the pvc glue cures for ~48 hours and then reestablish the filtration. That would cause havoc and break my back.

So I am cycling the rocks and sand in trash cans and buckets. The sand and rocks will be seeded with the beneficial bacteria. I will be adding Chaeto from my current setup into the new setup and mixing water. This, I hope, will avoid the cycle detrimentally effecting my other, established tanks.

Dry rock cycling in a 10 gallon trash can
Dry rock cycling in a 10 gallon trash can

Live sand cycling in a 5 gallon bucket
Live sand cycling in a 5 gallon bucket

Continue following this build to find out if it works. As always, I’m happy to be the guinea pig so you don’t have to!

Like, share, and subscribe; leave questions in the comments or reach out to me directly.

Happy reefing!

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