Setting up your first aquarium? Congrats, you’re taking the first steps into an exciting hobby that gives you the unique opportunity of bringing a slice of underwater nature right into your living room. But don’t forget to cycle your tank before adding fish!
If you’re not sure what “cycling” an aquarium means, it’s very important to keep reading below. Failing to complete this crucial step puts all your fish and other livestock at an almost immediate risk of death. Not a good start to your aquatic adventure, but luckily, it’s easy to avoid.
What is the nitrogen cycle?
When you put together an aquarium, you’re building an aquatic ecosystem from the ground up. Everything from the decorations, to the sand or gravel, to the kinds of livestock that will be calling your aquarium home is in your hands. It’s a lot of responsibility!
If you’ve just bought all your aquarium supplies, it can be tempting to fill the tank right up and bring home some fish. STOP! There is another step you need to complete before you do this: establishing a stable nitrogen cycle. Skipping this will cause “new tank syndrome”: the aquarium water becoming TOXIC to living beings.
If you’re not familiar with the nitrogen cycle, we highly encourage you to carefully read the information below. It’ll help you keep your fish alive and can prevent a lot of disappointment. The basics are more or less the same for both freshwater and saltwater aquariums.
How does the nitrogen cycle work & why do we need it?
You may have learned about the nitrogen cycle, a natural process that forms the backbone of pretty much all ecosystems on earth, in high school biology class. In the aquarium, it’s what turns waste toxins, namely ammonia, into much less harmful compounds that you can then remove from your tank.
Basically, every fish, coral, or invertebrate that goes into your tank has to eat. As they metabolize the proteins in their food, nitrogenous waste is produced. Most of this is excreted into the water as ammonia; fish, for example, release ammonia through their gills.
The problem is that ammonia is toxic to living beings (hence why their body has to get rid of it!). Even in small concentrations, its presence in the water can quickly cause illness and even death in your aquarium’s livestock.
But fear not! This is where the nitrogen cycle comes in. Basically, thanks to different species of bacteria, which we collectively refer to as “beneficial bacteria” in the aquarium hobby, this cycle converts ammonia into less toxic compounds. These can then be removed manually through a simple water change.
Ammonia to nitrite to nitrate
The “beneficial bacteria” (BB) in our aquariums can, with a little help on our part, establish themselves in the tank’s filter, substrate, and also in live rock in saltwater tanks. Basically any porous material is prime BB real estate.
From here, they work their magic.
- Ammonia is excreted by fish and other livestock
- One species of beneficial bacteria (Nitrosomonas) eats ammonia and converts it into somewhat less toxic nitrites
- Another species of beneficial bacteria (Nitrobacter) eats nitrite and converts it into less toxic nitrates
- In the wild: plants, microorganisms, and algae eat nitrates and grow. In turn, they are eaten by fish, starting the cycle all over again
- In the aquarium: any nitrates that are not absorbed by live plants or algae are removed by you, the aquarist, by means of water changes
As you can see, thanks to the BB that make the nitrogen cycle possible, your fish don’t have to swim in their own toxic waste. The bacteria create a safe environment that your livestock can thrive in.
How to cycle an aquarium
Ammonia source
By now, it should be clear that no aquarium can thrive without a stable nitrogen cycle. Cycling the tank is step 1 for a healthy ecosystem, and it should never be skipped. So… how do you do it? It’s easy! You just need an initial source of ammonia.
There are three basic methods, of which we prefer the third one:
- Fish-in cycling: This involves getting a few cheap fish, like guppies, and letting those be the ammonia suppliers. Not very humane, as there’s a good chance the seed fish will suffer and even die.
- Ghost feeding: You can cycle an aquarium by adding fish food and letting it decay. This releases ammonia, kick-starting the cycle. You may have to supplement regularly.
- Pure ammonium chloride*: You can find bottles that are free of soaps, fragrances, and surfactants for cheap at most hardware stores. This allows you a high degree of control.
*Toxic! Don’t inhale and don’t let it touch your skin. Keep away from children.
If you already have a healthy tank, you can greatly speed up the process by placing some of its filter material in the new tank’s filter. You can also buy bottled beneficial bacteria, but be sure to verify they’ve been kept refrigerated and aren’t out of date.
Remember to use dechlorinated (conditioned) water for anything aquarium-related, and to keep the protein skimmer off in marine tanks until the cycling process is done.
Let’s cycle!
Once you’ve decided on your ammonia source, add enough to get a reading of 1-2ppm on your liquid test kit—or a reading of “TOXIC” on an ammonia alert if you’re using it.
We recommend testing daily so you can see the cycle happening in real time:
- Initially, the ammonia levels will stay put. Supplement if they drop.
- After 2-4 weeks, the ammonia level will drop more quickly after adding, and you’ll start seeing nitrite readings. Keep supplementing ammonia.
- After 2-4 more weeks, you’ll start seeing nitrate readings.
💡 As the tank cycles, the pH level can drop, especially in saltwater aquariums. This can slow down the cycling process. Test the pH regularly and consider using a gentle buffer or doing a water change to get it back up if it drops too low.
Success!
You’ll know the tank is cycled if, after adding ammonia, you can come back 24 hours later with your water test kit and find zero ammonia and zero nitrite (but significant nitrate readings). How long this takes depends on many factors, including temperature, so be patient.
Congrats! At this point, you’ll have created a strong foundation for your tank’s filtration. Remember to keep the nitrate levels down by means of regular water changes. Perform water tests often to make sure everything is still in order, especially after making changes like adding new fish.
You may now go forth and purchase fish.
Did you know? The amount of beneficial bacteria colonizing the filter and substrate depends on the amount of waste being produced in the tank. You should avoid adding a lot of fish at once for this reason. Don’t overstock the tank either, because there’s a limit to the bioload your BB can handle.
Conclusion
Cycling an aquarium is a crucial, but oft-overlooked step. Without a stable nitrogen cycle, your fish are at risk of disease and even death. Establishing this cycle is done by adding ammonia to kickstart the process.
Dreaming of an aquarium for your home or business, but feel overwhelmed by the chemical processes involved? Or maybe you just don’t have the time? That’s where we come in. The FantaSEA Aquariums team can design, maintain, and set up any kind of freshwater or saltwater tank for you. Contact us with your ideas today!
Sources & further reading
Ip, Y. K., & Chew, S. F. (2010). Ammonia production, excretion, toxicity, and defense in fish: a review. Frontiers in physiology, 1, 134.
