Imagine an aquarium as a tiny, self-contained world. For fish to thrive, that world needs to be balanced. The key to that balance? Cycling.
Cycling is the process of establishing beneficial bacteria in a new aquarium. These bacteria are essential for converting harmful fish waste into less toxic substances. Skipping this process can be deadly for your fish.
When we talk about “cycling fish,” we’re referring to a method of aquarium cycling that involves using fish to start the process. This article will explain the nitrogen cycle, why cycling is so important, discuss both fishless and fish-in cycling methods, and offer tips for successfully cycling your aquarium, whether you choose to cycle with or without fish.
Understanding the nitrogen cycle
Before you add any fish to your tank, it’s vital to understand the nitrogen cycle. This cycle is a natural process that breaks down harmful waste products, keeping your fish healthy and your aquarium water clean.
The three stages of the nitrogen cycle
- Ammonia production: Fish waste, uneaten food, and decaying plants all produce ammonia (NH3), which is highly toxic to fish.
- Nitrite conversion: Beneficial bacteria called Nitrosomonas convert the ammonia into nitrite (NO2). Nitrite is also toxic to fish, but less so than ammonia.
- Nitrate conversion: Another type of beneficial bacteria (Nitrobacter) converts the nitrite into nitrate (NO3). Nitrate is much less toxic than nitrite and ammonia, but it still needs to be managed through regular water changes.
The role of beneficial bacteria
The goal of cycling is to grow a healthy colony of these beneficial bacteria. These bacteria act as a natural biological filter, keeping the water safe for your fish.
Why cycling is important for new aquariums
Cycling a new aquarium is vital for the well-being of your fish. Here’s why:
- Preventing “New Tank Syndrome”: Without cycling, ammonia and nitrite will quickly build to toxic levels. Fish living in these conditions will develop “New Tank Syndrome,” which is often fatal.
- Maintaining Water Quality: Cycling keeps the water safe and stable. The cycle is complete when ammonia and nitrite levels are at zero, and you can detect some nitrate.
- Long-Term Health of the Ecosystem: Cycling establishes a balanced environment where fish can thrive over the long term.
Fishless Cycling: The Recommended Method
Most aquarium experts recommend cycling your tank without fish in it. This gives you a chance to create a healthy biome without subjecting any fish to dangerous levels of ammonia and nitrites. Here’s how it works:
Setting Up the Tank
Get all your equipment together — tank, filter, heater, substrate, and any decorations you plan to add — and put it all in place. Fill the tank with water, making sure you’ve dechlorinated it.
Adding an Ammonia Source
Now you’ll need to add ammonia to the water to kickstart the nitrogen cycle. Pure ammonia is the most controllable option. Add a measured amount to the tank, targeting ammonia levels of 3 ppm (parts per million). Some people go as high as 5 ppm. You can also use fish food or a decaying shrimp, but it’s harder to control the levels this way.
Monitoring Water Parameters
This is where your aquarium water testing kit comes in. You’ll need to keep a close eye on ammonia, nitrite, and nitrate levels. Watch for the ammonia to spike and then fall, followed by a rise and fall in nitrite levels. Finally, you should see nitrate levels start to rise.
Accelerating the Cycle
You can speed things up by “seeding” the tank with beneficial bacteria. Add filter media from an established tank or use a commercial bacterial additive designed for aquariums. Also, make sure your water parameters are in the right range. Aim for a pH between 7.0 and 7.8 and a water temperature between 83°F and 87°F.
Completing the Cycle
The cycle is complete when your ammonia and nitrite levels consistently read 0 ppm. You’ll still have nitrates in the water, so perform a partial water change to reduce those levels before you introduce any fish.
Fish-in Cycling: Risks and Mitigation
Putting fish into a new tank before it’s cycled comes with serious risks. Here’s what you need to know before you decide to cycle your tank with fish inside.
The Dangers of Fish-in Cycling
- Ammonia and Nitrite Toxicity: During the cycling process, fish are exposed to dangerous levels of ammonia and nitrite.
- Stress and Disease: Those toxins can stress the fish, making them more likely to get sick.
- Potential Death: High levels of ammonia and nitrite can kill your fish.
When Fish-in Cycling Might Be Considered
Fish-in cycling should only be done in a true emergency, when you have no other choice. For example, you might consider it if you suddenly have to take in a fish and don’t have a cycled tank ready. It might also be a consideration if you don’t have the resources to do a fishless cycle.
Minimizing Harm During Fish-in Cycling
If you have to cycle with fish in the tank, here’s what you can do to make it less dangerous for them:
- Hardy fish: Start with just a few hardy fish that can tolerate changes in the water conditions. A good rule of thumb is to use “1 small fish for every 10 gallons of tank water.”
- Frequent water changes: Do partial water changes (25-50%) often to keep ammonia and nitrite levels down. A good starting point is to change 10 to 20 percent of the water during cycling. If ammonia or nitrite levels go above 0.2 ppm, do a partial water change.
- Monitor water parameters: Test the water every day or every other day, and change the water as needed.
- Limited feeding: Feed the fish very little, so they produce less waste.
Ethical Considerations
Before you start a fish-in cycle, think carefully about whether it’s ethical to put fish in potentially harmful conditions.
Alternative cycling methods: Plants and substrates
There are a few other ways to cycle a fish tank besides the methods mentioned above. Some aquarists have had success using live plants or established substrates to jump-start the cycling process.
Cycling with plants
Live aquatic plants can absorb ammonia and nitrates, creating a healthier environment for your fish. Diana Walstad, author of Ecology of the Planted Aquarium, says aquatic plants may actually consume nitrogen waste even more efficiently than bacteria.
If you’re going to try cycling with plants, plant the aquarium heavily before you add any fish.
It’s also important to make sure the plants have enough nutrients and light to thrive. When cycling this way, do a partial water change of about 30% each week.
Using established substrates and filters
Another way to speed up the cycling process is to transfer substrate or filter media from a healthy, established aquarium. This can rapidly introduce beneficial bacteria to your new tank. Even so, you’ll still need to monitor the water parameters closely to make sure the cycle is progressing as it should.
Summary
Cycling your aquarium is absolutely essential. Without it, you’re setting up your fish for a toxic environment. Establishing that beneficial bacteria colony is the key to a healthy, thriving tank.
Fishless cycling is the kindest, safest way to go. Why put your fish through the stress of high ammonia and nitrite levels when you can avoid it altogether? It takes patience, but it’s worth it.
Once your tank is cycled, don’t get complacent! Keep a close eye on those water parameters. Regular water changes are a must to maintain a healthy balance and keep your fish happy.
With proper cycling and ongoing maintenance, you’ll be well on your way to enjoying the fascinating and rewarding hobby of fishkeeping.