Patience & The Nitrogen Cycle

How To Cycle Your Tank

While talking to customers, or reading forums on the Internet, I often hear about using fish to start the nitrogen cycle in a new tank.  We recommend against using live animals to initiate this cycle, because of the harmful nitrogen compounds generated during the first phases of preparing your tank for life.  Here are some guidelines to help you establish your aquarium safe, efficient manner.

First and foremost, DON’T BUY FISH UNTIL YOUR TANK IS CYCLED! It’s not fair to the fish; sure, your first fish can be a guinea pig after the tank’s cycled, but please don’t use your fish to kick off the cycling.  Any ammonia-generating matter will begin the cycle.

Let’s talk about why a tank cycles, and what it means. This will help you understand the steps involved in maintaining a healthy aquarium. There are three types of filtration: mechanical (filter pads, floss, etc); chemical (activated carbon, phosphate pads); and biological, which is the one we’re concerned with when it comes to tank cycling. Biological filtration is a process where bacterial colonies that reside in the tank process nitrogenous compounds, with the end result being nitrate (remember, ammonia’s a nitrogen compound, too).

When you set up a tank – or when you move an existing tank – the bacterial colonies have to establish themselves at a population level that can effectively deal with the nitrogen produced by the life in the tank. So, the first thing you have to give them is a place to live. In saltwater, this is accomplished with live rock and aragonite sand. Freshwater, well, that’s why we have biowheels and bioballs and ceramic rings, all places with surface area for the bacteria to set up shop.

It’s possible to cycle a tank without adding anything – no ammonia, no bacteria, nothing. The reason is that the death of the bacteria living on the walls of the glass will generate enough ammonia to start things up. But, there’s not a lot being generated, so this method ends up taking the longest time for the cycle to complete (the bacteria won’t start their reproduction cycle until copious amounts of NH3&4 are available). If you’re doing saltwater, your cured live rock and sand contain enough organisms to kickstart the cycling process, and it’s usually not necessary to add an ammonia compound.

Before discussing the best method of cycling, let’s cover what these bacteria, our biological filters, actually do. There are not one, but two colonies of bacteria living in our tanks. First, is Nitrosomonas. These are the guys that eat ammonia. If you have a healthy colony of nitrosomonas, then your ammonia levels will never exceed trace amounts. Nitrites, like ammonia, are poisonous to your fish. Where does the nitrite come from? It’s the waste product of nitrosomonas. Good thing there’s another bacterial colony, called nitrobacter, that loves to chow down on nitrites. Their waste is nitrates, the least poisonous of the nitrogen compounds in your tank.

That’s why it’s called the nitrogen cycle: ammonia is converted to nitrite which is converted to nitrate. This cycle is a continuous process in your tank. The problem is when the cycle begins, and the colonies have to become established, there are large amounts of very bad things being generated in your tank. First, ammonia levels spike, until the bacteria propagate enough to overcome and absorb it. Then, nitrites bloom, and nitrobacter gets its chance to establish. Finally, when nitrates are high, you’ll see an algae bloom, as the ever-present spores set up in your tank and chow down on the nitrate.

As mentioned, you do not want fish in your tank while this is happening. Here’s how to get a strong nitrogen cycle started without harming your animals:

    Set up your tank, get your substrate in, fill it with RO (or treated) water, add your decorations, rock, aquascaping, etc.

    Take a piece of table shrimp, uncooked (and unseasoned), and toss it in the tank. As it rots, the ammonia it gives off will feed the nitrosomonas. (This is a “kickstarter”, and is not necessary.  It’s useful when you want to generate a large ammonia spike.)

    Pick up some of Seachem’s Stability at your LFS. This stuff is bacterial gold in a bottle, and they don’t charge gold prices like some of the other supplement makers. Dose with Stability as per the instructions for a new tank.

    Wait. Seriously, just make sure the water’s topped off and the equipment is operating normally. If you have bio-surface area, like floss, balls, etc. now’s the time to get them in your filter (or cartridge, whatever).

    Wait some more. It can take from five days to two weeks for the cycle to complete. If the bacteria have nowhere to live (no surface area), it can take a month or more, and then it’s still possible the colonies don’t grow large enough to support tank life. Make sure you have a place for them to live.

    At some point in the process, you’ll notice the beginnings of life in your sterile tank, in the form of an algae bloom. This is a sign that the cycle is nearing completion – there are enough nitrates in the tank to support algae.

    Get your water tested; either do it yourself, or have your LFS test it. There should be trace ammonia, zero nitrites, and somewhere around 20-40ppm nitrates. Yay! Your tank is cycled!

Before you add life, do a 50% water change (25% on 75+ gallon tanks), and dose again with Stability.

At this point, you can get you some critters in your tank. Saltwater, start with a cleaning crew – turbo snails, margarita snails, nassarius snails, hermit crabs, etc. Freshwater, add mystery snails or malaysian burrowing snails, some plant life (hornwort, java moss, anachris, etc), and your first fish.

To keep your tank healthy, you’ll need to determine your water change schedule. The frequency and amount of the change are dependent on the bioload in your tank. If you have a bunch of young, hungry fish you feed twice a day, then you’ll be doing 20% weekly water changes. If your tank is a sparse community tank, you could get away with changes every two weeks, or maybe even monthly. Here’s how to determine your schedule:

Start by performing a 10% water change weekly. Try to be consistent (every Sunday night, for example). Twenty-four hours or so after your change, test the nitrates in your water. It will take at least a month of weekly changes and tests to determine if your nitrate levels are creeping, or if the weekly 10% is enough to maintain them in the safe zone. If you notice, after a month, that the nitrates aren’t staying below 20ppm, then you’re running a high bioload and you need to increase your frequency or amount. However, if your nitrates are zero, or hover near there, try reducing to 10% every two weeks (or 5% per week), and continue to monitor. If they start climbing, then go back to the previous weekly schedule.

If you have any questions, just email us ( or call the store at 406-585-1151. Remember to be patient, don’t put fish in your tank until it’s ready,, and stick to your water change schedule.  It’s that easy to have a healthy, natural aquarium.

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