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Fishless Cycle

Cycling Your New Aquarium Without Fish

(The First Tank Guide)

What is Aquarium Cycling?

Cycling your aquarium is the process of establishing the biological filter, a colony of beneficial bacteria that live in the filter media and process the fish's waste. The effects of the cycling process on fish are sometimes referred to as "New Tank Syndrome." New Tank Syndrome can sometimes be avoided by cycling the tank without fish. However, New Tank Syndrome can always be avoided by properly cycling your aquarium with a small number of fish and keeping up with the necessary extra water changes.

How Do I Cycle MY Tank Without Fish?

To cycle your new aquarium without using fish, you need to set up your new aquarium, make sure all the equipment is functioning and that nothing leaks, and then dechlorinate the water. Then you add some ammonia to the tank. Make sure you use an ammonia that does not have any added colors, perfumes, detergents or anything else that could be harmful to your fish, your biological filter, or any of your equipment.

You want to add enough ammonia to the tank to get your concentration pretty high, probably around 4ppm or more, well into the "danger" zone on most test kits. This can be done either by adding a few drops of ammonia each day until your tank reaches this level, then continuing to add more ammonia to the tank daily until the nitrite levels reach 0ppm and stay there, or by adding a lot of ammonia all at once and letting the tank sit, only beginning to add more ammonia to the tank when the ammonia level begins to drop.

How Do I Know If There Is Enough Ammonia in the Tank?

With fishless cycling, you will need to do a lot of testing. To start with, you will need to test for ammonia daily to see what your ammonia level is, and whether or not you need to add more ammonia yet. Once the ammonia levels in your tank begin to drop, you will need to add more ammonia daily until the nitrite levels stay steady at 0ppm and you are ready to get fish. So, once your ammonia levels start to drop, you have to start testing for both ammonia (to make sure the levels are staying up) and nitrite (to watch for the increase and then decrease in nitrite levels).

Remember, it is vitally important to the process that you not let the tank reach 0ppm ammonia before you add your fish. You'll need to test for ammonia at least daily once the ammonia levels start to drop.

When Is My Tank Ready for Fish?

Your tank is ready to add fish when your ammonia tests are quickly dropping over the course of a day, and your nitrite level has risen and subsequently dropped back to 0ppm.

Once you reach this point, you are ready to add your first fish. However, before you add your first fish, you need to do a water change to eliminate excess nitrate buildup in the tank (since you have been neglecting your regular water changes up to this point) and to remove the extra ammonia you have been adding. This will usually be a 50% or greater water change.

After you perform this large water change, you have just a few hours to get fish into the tank to start producing waste to keep the biological filter healthy.

What Are the Drawbacks to Fishless Cycling?

This is a topic you won't see covered in many places, especially those that are promoting fishless cycling.

There are several drawbacks to fishless cycling, especially for a beginner.

There are a number of other processes that go on in the tank and the filter that this process doesn't address, primarily handling of other organic material produced in the fish's metabolism. In fact, the high ammonia levels you have maintained in the tank can prevent some of these other processes from starting, even if there is a waste source for them to use (such as decaying fish food or a piece of meat). Of course, adding another waste source to the tank could result in a messy, cloudy, or otherwise unsuitable aquarium environment. Also, the high ammonia levels will keep the oxygen levels low, preventing the filter from operating at a good efficiency.

Often, when cycling a tank without fish, you lose the biological filter between when you think the filter is ready and when you get fish, meaning after going through several weeks without fish in the tank to get the tank cycled without fish, you introduce fish to an uncycled tank anyway, resulting in stress and losses.

Also, since some of the other processes that are not ready when you introduce fish because you haven't had fish and fish waste in the tank are not ready, which can cause problems, leaving you with the same process you would have gone through with a limited number of fish and a lot of water changes, or significant risk to your fish when you do get fish.

On top of that, you need to do a lot of testing, learn how to read the test results, and understand what the tests are telling you. This shouldn't really be necessary when cycling with fish. If you cycle with fish, you may want to get the water tested once or twice during the process (though it isn't really necessary), but usually a pet shop will do that free or cheap. Even when you are testing your tank while cycling without fish, you're often going 8-16 hours between tests, leaving enough time for the filter to significantly collapse.

On top of all this, if you are cycling with fish and keeping up with the water changes, the fish will indicate stress to you much sooner than you'd read it on a test kit - and they'll actually indicate stress to you, rather than a test that says that there may be a stressful level of ammonia or nitrite in the water - and you can quickly correct this potentially stressful situation with a water change. Of course, if you are keeping up with the necessary water changes and aren't using too many fish, your ammonia will never reach a stressful level while the tank is cycling.

Why Is It Better to Cycle with Fish?

Cycling the tank with fish always results in a cycled tank (assuming the tank is large enough to cycle), but cycling without fish may or may not leave you with a cycled tank, and the only way to tell is to add fish.

Cycling the tank with fish minimizes the work you need to do, and minimizes the things you need to do and understand to get your tank running and stable.

Cycling the tank with fish poses little, if any, risk to the fish, assuming you follow three simple rules: few fish, minimal feeding, and plenty of water changes. Cycling the tank without fish may pose no risk to your fish, but may also pose much greater risk to your fish than cycling with fish.

Why Are Some People Against Cycling with Fish?

Most people who are adamantly against cycling a tank with fish are thinking of the bad old days (or anyone who visits PetsMart, PetCo, or other bad pet shops) and gets the recommendation to just dump a bunch of feeder goldfish (I've heard as many as two fish per gallon of water) into the tank to cycle it, and not to do any water changes for one to two months. This is very, VERY bad advice, and certainly would not be recommended by anyone who is interested in the stability of your tank or the well being of the fish in question. And, yes, fishless cycling is almost certainly better than that approach. However, cycling with a small number of hearty fish and keeping up with the water changes is definitely going to be easier, less frustrating, and pose less risk to your fish than fishless cycling.

Check out these pages to help you get started with your first fish tank:



"Thanks very much for your time, by the way. I enjoy reading your website, as it's full of useful information."
January 20, 2011
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"Wow, Keith, that was a fountain of knowledge! Thank you so much! It's too bad I didn't get more information at the pet stores I went to."
April 18, 2016
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