Basic Cycling Info

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Staff member
Dec 30, 2005
Real Name
Mr. Normal
So You Have A Fish Tank!!
(A Cycling Overview)

Did you also get some fish at the same time? Or maybe the school gave them to you since it is now the end of the year. Grandpa and Grandma brought you a present? Or you just could no longer listen to the begging from your children and gave in.

Even if a planned evolution, or an abrupt circumstance that you find yourself in, some of the information here may help you and your new pets.

In The Old Days

And even sometimes today, by ill intent or misconception, you will hear, “ fill the tank, treat with this and let it age for a couple of days” or “ this will let you add fish today”. Only if it was that simple, not to imply that this will be hard, but you have to remember, you are establishing a microenvironment. Basically, creating a small-scale world for living creatures.

You will not find the fix or set up in a bottle, and then add another two or three items to “get” the water to where “they” think it needs to be. With some cautious steps and easy preparations you can create the suitable environment for your fish.

“Cycling A Tank”

What we mean by this term, is the process of establishing an environment that will beneficially support fish life, with minimal stress to the fish and to you. The terms used here are relevant to the “nitrogen” cycle and how it relates to the aquarium.

The first item for discussion is Ammonia (NH3). All decaying matter, like uneaten food and from fish wastes, produces this. Any detectable amount is trouble for your fish, and levels of .25 ppm and above can damage fish permanently, based on length of exposure. This damage occurs to the gills, and causes breathing problems. It will damage the gills whether the fish live or die.

Secondly, the bacteria that break down ammonia produce Nitrite (NO2). This nitrite blocks the ability of blood to absorb oxygen. Even if the fish can breathe, they are not able to utilize the oxygen they take in, as easily. They can act as if panic-stricken and/or have little control over their movements. Even with short-term exposure at high levels, stress occurs and they may not be able to ward off other immune system attacks.

And finally, second bacteria forms that consume nitrite and forms Nitrate (NO3). While short-term exposure to low levels of Nitrate are not a concern, they can be if too high over a long term. Nitrates are removed with consistent regular water changes or by aquatic plant life.

A cycle is never really complete. It is established and an ongoing evolution. Keeping this “cycle” balanced and continuous is the goal of properly maintaining a tank for a healthy environment for your fish. Strive for Zero Ammonia, Zero Nitrite, and approximately 20 ppm Nitrate or less.

Ways To Cycle Your Tank

I have broken them down into three currently widely accepted methods.

(1) Using Established Bio-Logical Filter Media

This is probably the most preferred and least stressful method that will allow you to stock your fish quickly and depending on the extreme you use, to full tank load.

If you have established tanks already, without any issues, you can put filter media in them before the new set up is ready. The biological bacteria can establish themselves on it and it can be transferred to the new tank and fish added. This can be as simple as sponges on filter intakes, filter cartridges in HOB/HOT, or media in canisters. It can include substrate or décor from other tanks, such as rocks and plants.

Please ensure the tank you are drawing from, has Zero Ammonia, Zero Nitrites and less than 20-30 ppm Nitrates. It should also be a tank free of disease. Do not take media or filter squeezing from tanks you are not sure of or from a local LFS. You could be establishing your new tank with all kinds of problems. Since most bacteria will not be free floating in the water column, taking just the water will not accomplish much.

The bacteria that maintain the cycle need to be fed in order to maintain. Waiting a few days can be disastrous. If moving a tank, keep the media wet in the old tank water, aerated and for the short term only.

This method provides minimal stress to the fish, minimal work on your part, quick stocking, at or near full capacity. But you must plan ahead. It could take several weeks to establish a bacterial colony of sufficient size, on the media you move to the new tank.

(2) Fishless Cycling

Just as it sounds, you can establish the cycling environment without any fish. This method does not pose any threat to fish, establishes a large bacteria colony allowing full stocking upon completion and gives you time to decide on what fish you want.

When establishing a tank with this method, you will use a source of ammonia to initiate the nitrogen cycle. After your tank is set up, add water and treat for chlorine/chloramines. Your filtering systems and heaters should be in place and operating to your satisfaction.

Add ammonia to bring the tank to a concentration of 5 ppm. The amount you add will vary with the size tank you have. Do not be in a rush. Add small amounts and test, repeating as necessary. If you get it too high, you can drain and refill.

Now the hurry up and wait part happens. Every two days, test your ammonia level in the tank. When the ammonia levels start dropping, add additional ammonia as required to keep the ammonia at 3-4 ppm, start daily testing and test for ammonia and nitrites. Nitrites should be developing as ammonia goes away. This first stage could take 1-3 weeks.

When you see the test results showing Nitrites, start maintaining your ammonia at the 2-3 ppm range. The nitrites increasing reflect you are in to the second stage. Continue daily testing for ammonia and maintain the tank in the 3 ppm range. You will see nitrites climb so high they will be off the scale for a reading. This will continue for one to two weeks and it will seem the nitrites are never going to go away.

There will be a day where you test and the nitrites have completely disappeared, thus, the bacteria that convert them to nitrates have established themselves. When you see this drop to zero on nitrites, dose ammonia in the tank to about 5 ppm, and wait 24 hours. If at the end of that period, ammonia and nitrites are zero, your cycle has been established. Test for nitrates, and do a 75-90% water change. Pull your water down to 20 ppm nitrates and add the fish! If you have to wait to get your fish, keep the cycle established by dosing more ammonia, but you may have to do another water change before adding your fish.

(3) Fishy Cycling

This method is probably what many fall into from all the myths that run rampant out there. It is also the method that can cause severe stress or death to the fish. There are some simple techniques that make this type of cycle go easier, but take some pre-planning on your part.

The basics of this method are to set up your tank, fill, treat with a water conditioner, add some hardy fish that can handle stressful conditions, test/monitor the ammonia and nitrite levels, and do water changes as necessary.

When your cycle is established, you have a bacteria load that can handle the fish that are in there presently. More fish can be added in small numbers over a period of time, allowing for a mini-cycle to grow the bacteria levels to the new bio-load. You need to pay constant attention to your tank, testing daily, doing water changes when required, not when you can get around to it. Do not assume that you can add more fish just because reading are undetectable or low. Give the environment time to respond.

You will be captive to testing at least twice daily, doing water changes whenever ammonia or nitrites hit .25 ppm. Do not be surprised that even with a cautious approach, you lose some fish.
When you understand the above and your questions have been answered, please ask for:

Part II The Nitrogen Cycle In Depth

Part III Established Media Transfer Cycling

Part IV Fishless Cycling Details

Part V Fishy Cycling Details

Part VI Other Options And Methods

Part VII Tank Water Chemistry

The above article was to give a previously uninformed person a general overview on setting up the bacteria cycle required to establish a tank. It was from a generic standpoint without excessive detail to keep interest and take things in small steps. I hope it was beneficial for you.

Bob Bishop
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