A number of years ago I wrote some well received articles for a Goldfish forum that I was a member of, and I recently discovered that the forum, sadly, no longer exists. I was able to retrieve my articles, using an online “wayback machine” and would like to post them here to access for anyone who might be interested.
Both articles, this one and the “Guide to Cleaning Aquarium Filters”, are relevant not only to fancy goldfish enthusiasts, but to all freshwater fish keepers and ponders alike.
Guide to Cycling an Aquarium
by Ci Shepard
Jan/2014
First of all, let's get an understanding of what "cycling" an aquarium actually is. More correctly described as the nitrification cycle, the process consists of growing certain types of beneficial bacteria on the surfaces inside your tank and filters. These bacteria consume waste products produced by the aquarium inhabitants which is primarily ammonia. Other waste products, such as feces, excess food and plant debris should be removed regularly, but if left in the tank, they will break down and give off ammonia as well.
The type of bacteria that oxidize ammonia as part of their metabolic process are called Nitrosomonas. They consume the ammonia and change it into nitrite. When nitrite appears in the tank another bacteria, called Nitrobacter starts to grow and these oxidize nitrite into nitrate. Both of these types of bacteria will appear in the tank eventually if ammonia is present - it is impossible to know where they come from - the air, the tap water, the dust and microbes on the equipment. They just appear and form colonies, but there are ways to help them along which I will address later in this article.
Both ammonia and nitrite are toxic to fish. Nitrate is not harmful to fish until it reaches high levels.
(Newcomers to the world of testing sometimes confuse the words 'nitrite' and 'nitrate' because the spelling is so close. Pay attention to the vowels to understand properly!)
So, when a fish tank "cycles" it is going through the process of growing bacterial colonies to consume toxic waste products in the aquarium. The process looks something like this:
Ammonia is added to water every day ---- Nitrosomas grow ---- they start to convert some of the ammonia to nitrite ---- Nitrobacter grow ---- they start to convert it the nitrite into nitrate. Eventually, there is enough bacteria to convert all the ammonia and nitrite in the tank every minute of every day, so that whenever you test for them, the number reads as zero.
If you test the water every day during this process, you will see the ammonia build and then "spike" (reach a high point) and then start to go down, and at that time you'll start to see nitrite readings. These will then spike as well, while the ammonia continues to decrease and nitrate will start to register on your test kit.
Eventually, the ammonia test readings will hit zero as the bacterial colony has grown to the point where it is consuming all the ammonia produced in the tank almost immediately.
The same will happen with the nitrite readings, and as they decrease to zero the nitrate readings will increase. The tank is considered "cycled" when you get readings of zero for ammonia and nitrite, and some reading of nitrate, and this stays consistent day after day with gradual increases in nitrate over time. The water is now safe for fish to live in and will continue to be so as long as you control the nitrates from reaching high levels, usually by doing regular water changes. If you have an aquarium with submerged live plants, or emersed plants with their roots in the water, these will consume nitrate and you can adjust your water changes accordingly.
The entire cycling process can take a few weeks to a couple months.
There are several methods of cycling a new aquarium or pond:
Fishless Cycle:
- Set your tank up with your filter of choice, heater, airstones, substrate and accessories (no fish).
- Acquire liquid drop test kits, like API brand (not dip strips as they are notoriously inaccurate) for pH, kH, ammonia, nitrite and nitrate.
-Fill the tank with dechlorinated water.
- Test your pH. Bacterial colonies grow best in a pH above 7. Test your kH. If you have a low kH (below 5 drops on the test kit) your pH may not be stable which stresses fish and inhibits bacterial growth. You may need to buffer (add kH) your water regularly to correct this. Adding baking soda with each water change will raise your kH and pH and keep it stable. 1/4 tsp of baking soda in 20 gal. of water will raise the kH one dkH (one drop on the test kit). Add small amounts at a time and test to see where your kH and pH are going. Keep track so you can add the appropriate amount of baking soda with each water change.
- Run your filters and aeration during the cycling process. Bacteria like oxygen rich water. Running a heater can also speed up the cycle, although it is not necessary. Most goldfish keepers do not heat their tanks, so you may not have planned on a heater, however having one on hand can be useful for a sick fish in a hospital tank, so you might consider adding one now and using it for cycling. Do use dechlorinator, as water with chlorine or chloramine will inhibit bacterial growth.
- Start the cycle by adding pure ammonia to the tank (look for brands that say "pure" or "clear" with no added scent, coloring or detergents. Shake the bottle, if it foams up, then it has added cleansers). Measure about 2 drops per gallon, add to tank and test the water. Keep track of how much you add till you reach the desired ppm (1-2 ppm if you plan on getting 2-3 fish, bump it up to 3-4ppm if you will be adding, say, 3-6 fish. Don't go over 5ppm, as excess ammonia can sometimes inhibit the growth of a bacterial colony)
- Test the water for ammonia every morning. It will stay at your chosen ppm for a while (from a couple days to a couple of weeks). When you see it starting to decrease, it means that bacteria are growing and "consuming" the ammonia. Test now for nitrite. You will start to see readings increase gradually.
- At this point, start adding ammonia daily, to keep it constant at your desired ppm. Continue to test once a day. It may take longer for the nitrite consuming bacteria to get established. You will see the daily nitrite ppm spike and then start to gradually decrease. You may also start to see your ammonia readings dropping significantly each morning, even reaching zero every 24 hrs. Keep dosing!
- As the nitrite readings begin to drop, you can start testing for nitrate. You are nearing the end. At the point where both ammonia and nitrite readings are at zero each morning, before you redose your bottled ammonia, and the nitrate number is building, you can consider your tank cycled. The process often takes 6-8 weeks but can easily be longer or shorter. There is no way to predict or control this length of time.
- Remember you chose your ammonia ppm level based on how many fish you wanted to introduce into the tank? The beauty of this method is that you now have an established bacterial colony large enough to support this number of fish, right away. If you are not ready to add your fish, keep dosing ammonia daily to feed the bacteria. When you are ready, stop your dosing the day before, and do a large water change to bring down your nitrate level and have clean fresh water for the fish. Add them all at once.
- Keep testing daily for a while. If you over estimated how much ammonia conversion you needed for the amount of fish you bought, no problem. The excess bacteria will die off - the colony will always adjust to however much "food" is available to them. If you underestimated, then you might see a small ammonia spike while more bacteria grow to consume the excess. You can do water changes daily to protect the fish, or you can dose with an ammonia binder/dechlor product like Seachem's Prime every other day till you start to see your numbers at zero again.
- You may read about fishless cycling using shrimp, fishfood and even urine. All of these items, when placed in the water, will start breaking down and produce ammonia, and the cycling process will happen. It is somewhat harder to control the ammonia values, but with some experimentation and a lot of testing, you should be able to reach your target ammonia levels and keep them there each day.
Pros for a fishless cycle:
- Completely safe for fish - no exposure to toxic ammonia or nitrite
- Tank can be ready for a full complement of fish all at once
Cons to a fishless cycle:
- Waiting a long time after setting up to add fish!
Cycling with Fish:
- In this method, live fish will provide the new tank with an ammonia source. The trick is to keep the fish safe from the toxins of ammonia and nitrite, while at the same time providing the new bacterial colony with enough "food" to get established. Some people use sacrificial fish - inexpensive feeder fish or some fairly hardy species like zebra danios and either discard or rehome them at the end or keep them on if they survive. Others simply get the fish they wanted in the first place and do their best to keep them safe.
- Most of the first steps are very much the same as in the fishless cycle. Set up your tank and turn on your equipment, purchase test kits and a product that is both a dechlorinator and an ammonia binder (such as Prime by Seachem). Use this product with your initial water fill, following the directions on the bottle, and add your fish but keep in mind that it is possible to lose some when you are choosing the number of fish and price point.
- The fish will start producing ammonia immediately. Feed the fish, but sparingly. Prime will 'bind' the ammonia and protect your fish from it's effects, but will leave it available for bacteria to utilize. Also, when using Prime, ammonia will still register on your test kits, so you can track the ppm. With live fish it is advisable to not let the ammonia build up past 1-2 ppm. Prime can be dosed every 48 hrs, and in theory can protect fish at higher ammonia levels, but the safety of the fish is paramount so appropriately sized water changes are usually incorporated to keep the levels down. Vacuum or syphon the tank debris each time.
- Some people advocate frequent 100% water changes during the cycling period, and this can work as well, since the types of beneficial bacteria we are seeking to establish are not free swimming in the water column. The colonies grow on all the hard surfaces that water comes in contact with, and are attached quite firmly - even rinsing and spraying with water won't dislodge them. There are some negatives to doing such large water changes, though. The nitrification cycle may take longer because you are regularly interrupting the bacterial colonies' source of food. Plus, unless you are using an ammonia binder in addition to the large changes, you are subjecting the fish to a yo-yo effect of ammonia levels which is stressful.
- As soon as you start to see nitrite values in your daily testing, it would be a good idea to add salt to the tank at the rate of 1 tsp. per 5 gallons of water. Salt will protect the fish from nitrite poisoning (also known as brown blood disease). Different brands of dechlorinator and water treatment products claim to bind nitrite as well as ammonia, but some feel that the science is questionable. This small amount of salt will do no harm, and is good insurance for the fish.When you do a water change, add more salt depending on how many gallons of new water you are adding. Keep the tank salted until it is cycled, then stop adding salt and let your water changes gradually remove it.
- The remainder of the cycling period is much the same as with the fishless cycle. Keep track of what is happening with daily testing and when your ammonia and nitrite numbers are consistently at zero, you are done. You can stop adding Prime every other day, stop adding salt, cut back on water tests and start establishing a regular water change routine.
- You can also add more fish, but bear in mind that you have only grown a bacterial colony of the exact size needed to consume the ammonia produced by your original fish. When you add new fish, the ammonia level will increase and the colony will need time to grow larger in order to match the new supply. You may see a measurable spike in ammonia and nitrite levels. For these reasons, it is advisable to only add one fish at a time, maybe two if they are small. Have your Prime ready and possibly salt the tank again ... testing will tell you what to do and when.
- Usually, when a cycle is set back by adding new fish, or for other reasons like accidental overfeeding, forgetting to add dechlorinator or rinsing filters with chlorinated water, or from medications and other chemicals that may cause a die off of bacteria, it does not take a lot of time for it to recover. The colony will grow faster than it did when starting from scratch. One more thing to note is that Nitrobacter bacteria (those that convert nitrite to nitrate) seem to be a bit more fragile than Nitrosomonas and will die back easier. You can easily have a spike in nitrite only, without a corresponding spike in ammonia.
Pros for a fish-in cycle:
Can enjoy fish right away
Cons to a fish-in cycle:
Extra care needed to keep fish safe from toxic ammonia and nitrite
Cycle can take longer
Can only add 1-2 fish at a time
Cycling Shortcuts:
Seeding with Established Filters:
If you have access to an already cycled tank or pond, that you trust to be disease and parasite free, you can 'harvest' some bacteria from it to jumpstart your new tank. This can work to shorten the time required for both a fishless and fish-in cycle, sometimes considerably so.
The best way would be to add some of the filter media, gravel or even ornaments from the established tank to the new tank. Another possibility is to take 'squeezings' from a filter sponge or mulm from the tank substrate and add that to your new tank. This dirty water will contain some bacteria, though probably not as much as from some plastic objects, ceramic or sponge filter media or gravel (remember that bacteria cling to surfaces).
Bottled Bacteria:
Most bottled bacteria products contain anaerobic bacteria that do not require oxygen to function. Even though the bottles claim that these products will aid in cycling a tank, they do not contain the aerobic bacteria needed for nitrification.
Anaerobic bacteria can digest organics and sludge in a dirty environment, and this can aid in reducing the amount of ammonia produced in these conditions, but that is not the case in a newly set up aquarium (or should not be!)
There are only a couple of sources for real Nitrobacter and Nitrosomonas bacteria which need to be refrigerated and shipped overnight with a cold pack in order to stay alive. It is an expensive way to cycle a tank, but effective and an 'instant cycle' can often be attained. Here are links to the two known companies that carry this type of product:
Another cycling method worth mentioning is used by planted tank enthusiasts. If you use a proper substrate, lighting, heat, and fertilizers required by aquatic plants and fill a tank with rooted plants right from the start, the tank can often be 'instantly cycled'. The plants themselves act as filters, consuming most of the ammonia. As time goes by, the filters and substrate develop bacterial colonies to take up the slack if needed.
The key to this method, though, is to plant heavily and stock fish very lightly, or not at all until you are sure the cycle is established.
Some aquatic plant substrates are designed to release ammonia as a nutrient source for the plants. You can also add bottled ammonia and cycle the filters as you would for a fishless cycle. Make a judgement call based on testing, plant density and desired number of fish.
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