The conventional method of using a hardy fish to cycle a new tank has some disadvantages. First, subjecting a fish, however hardy, to ammonia and nitrite stress may be unnecessarily cruel. Second, you have to have some use for the fish after the tank is cycled. Third, this hardy fish may bring in pathogens to your aquarium environment. 

Originally published as:
Koga, James S. Use Household Ammonia to Humanely Cycle a Tank1. Freshwater and Marine Aquarium, 19, no. 4 (December 1996): 213-214. 

An alternate method to using a hardy fish for cycling a tank is to move part of an established filter bed from another tank. This is an excellent method, which may reduce cycling time down to a minimal time period. However, many aquarists do not have the resources or the foresight (you have to have spare media cycling) to do this method. A disadvantage of this method is that any pathogens present in the donor tank may be spread to the recipient tank.

I would like to share what I believe is a better method than using a hardy fish, and one that may also hold some advantages over the donor filter bed method. This method is not of my invention, but I believe I have found some added practices that make for a fast, convenient, and humane way for cycling a tank. My experience is limited to freshwater tanks, so I can only say that this procedure should work with the freshwater  environment. This article is written for the the aquarist who already has some understanding of the nitrogen cycle. 

Some time ago, I came across a post in the Aquarium groups on the Internet that mentioned adding Ammonium Chloride to cycle a saltwater tank, and I believe the process is (or was) described in the marine FAQ files. Later on, I came across an article on Goldfish culture (Meyer). It recommended the use of household ammonia to cycle the tank. Instead of using a fish to produce ammonia, why not add ammonia itself?. 

The basic ingredients for cycling a tank are a starter culture of nitrifying bacteria (innoculum), ammonia, water, oxygen, and a substrate for the bacteria. I am assuming that your aquarium has been setup competently, so that it has water, biofiltration media (substrate), and aeration (oxygen). This leaves the ammonia and the bacteria. 

I use clear, unscented, no additives, 100% pure household ammonia from the supermarket. A quart costs less than a dollar and might last you for years. You will want to place it in a container that allows dispensing by drops. An old water conditioner bottle with the right type of top is good: BE SURE TO LABEL IT! Keep it out of the reach of children. Alternatively, some aquarium stores have started to sell bottles of Ammonium Chloride for this purpose. 

A starter culture of Bacteria can be added by two methods. Some material from an established aquarium can provide the needed innoculum: some water, a piece of used filter material, a decorative object, a handful of gravel. This shares the disadvantage of the donor media method of bringing in pathogens. However, if the donor tank has been in good health, there may be no compelling reason to avoid donor material. The second method is to use one of the commercial preparations of nitrifying bacteria. I have had good results with Hagen's Cycle (TM), but I note that there are many other products available, with more coming on the market all the time. 

One added factor not often mentioned is the temperature of the cycling aquarium. Both Nitrosomonas and Nitrobacter have optimal temperature ranges for growth and metabolism of 30 - 35 C (86 - 95 F) (Lawson, p. 234, and Johnson). Turning the temperature up to this range is not practical with fish in the aquarium, as it is above the suggested temperature for most tropicals (Mollys being one exception). However, since we are not subjecting fish to the rigors of higher temperatures, we are free to crank up the heater to the mid to high eighties (F), which is the range I use, and probably the highest I would ask my heaters to support. I have been able to cycle an aquarium in less than two weeks at this temperature. 
Ammonia Alert
Graphic from: Seachem.com
The method also requires some testing kits, mainly for ammonia and nitrite. One very convenient method of testing ammonia is a product from Seachem called the "Ammonia Alert"(TM). Essentially, it functions as an "ammonia gauge" The Alert is basically a plastic card, held onto the glass with a suction cup. On the card is a chemically impregnated spot that turns darker in the presence of ammonia. I use them in all my aquariums, and have found them to work well in my hard, alkaline water; I have had little or no experience with them in other types of water, so I cannot vouch for for them in all conditions. The following procedure is written for the use of the Ammonia Alert, but you may substitute your favorite ammonia test kit, if you prefer. 
Cell-Pore Airstone
Cell-Pore AirStone image
from cercona.com

1. Set up the Aquarium: filters, heaters, lights and all. Be sure to dechlorinate/dechoraminate the water. 

2. Place the "Ammonia Alert" in the aquarium. It usually needs a day or two to acclimate to the aquarium. 

3. Keep the filter running throughout this process. 

4. Provide extra aeration if possible. With an outside hang on-the-back power filter, a good way to do this is keep the water level a couple of inches lower than usual so that water falling from the filter makes a bigger splash than usual; the more bubbles breaking on the surface of the water, the more oxygen is in the water, and the bacteria need oxygen to grow. You can raise the water level when you are ready to add fish. Other types of filters may offer other aeration increasing options. Or, the addition of a simple airstone might suffice. 

5. If you can, try to keep the temperature of the water up in the low to high eighties (F) for reasons explained above. Remember to adjust the temperature back down to a livable temperature for your fish before adding them. 

6. Inoculate your aquarium with bacteria, either by placing some material from an established aquarium or use a commercial bacteria culture. I put a packet or two of Cycle"(TM) in the water. Wait about an hour. 

7. Put 3-5 drops of pure ammonia in the tank, or enough ammonia to turn the "Ammonia Alert" dark. If it doesn't darken, add more. Wait for the ammonia alert to go back to a "safe" level. This may take several days. Repeat this many times, each time waiting for the ammonia level to get back to "safe" before adding more ammonia... 

8. Continue to put ammonia in the tank until the "Ammonia  alert" shows that the ammonia level goes to zero within  8-12 hours after the ammonia is put in. Try putting some in the morning before work and checking when you get home. Once the tank shows the ability to lower the ammonia level in this time interval, this means that a large population of bacteria is resident in your filter. This may take 2 weeks or even more (even four weeks). 

9. While the ammonia level is at "safe", test for nitrites. If it shows zero nitrites, proceed to the next step. If it does not, go back to step 8 and repeat step 8 three to four more times and then test again for nitrites. 

10. Adjust the heater down to a livable temperature for the fish. Do a very large water change (about 90%), and then  you are ready to add fish: you can go to the fish store now. (Remember, only add dechlorinated water of about  the same temperature to the tank in order not to stress the bacteria with too drastic a change.) 

. .
There you have it: a method that grows beneficial bacteria  that does not call for the stressing of a hardy fish. Also,  this method can be easily modified to keep a vacant tank cycled. I hope it serves you well in the future.

Johnson, Erik L. July 1993. Turn Up the Heat! Tropical Fish Hobbyist XLI (11): 80-81. 

Lawson, Thomas B. Fundamentals of Aquacultural Engineering. New York, NY: Chapman and Hall, 1995. 

Meyer, Stephen M. November 1993. Goldfish From the Beginning, Part II. Aquarium Fish Magazine, 6(2):32-42. 

[End Original Article]


In the time since this article was originally published, I've realized that there are some things missing from this article that would have made it a lot more useful. Also, some other experiences with the method have been reported. So here we go:

1. The label on my bottle of ammonia says it contains: "pure ammonia"; despite this, household ammonia in the U.S. is mostly water.  It is a solution of ammonium hydroxide (also called "aqueous ammonia"). The strength can vary between 5 to 10 % ammonia (that's 50,000  to 100, 000 ppm). Meyer's latest publication about this method (see below) states that since the concentration of household ammonia can vary, it's best to experiment until you bring the initial level of ammonia in the tank to 1-2 ppM. He suggests starting out with a 0.25 teaspoons (which would be about 1.25 mL) for a 20 gallon tank.

Ammonia Alert
Graphic from: Seachem.com
2. In the article, I stated that I added enough ammonia to turn the Ammonia Alert dark. Although this is what I actually do, that statement is not exactly way up there on the scientific precision scale. In looking at the instructions for an Ammonia Alert, the following concentrations are indicated by the levels of darkness:
SeaChem Ammonia Alert Levels
Status Label  Color (~) Free Ammonia Level (ppm)
Safe Yellow ~0.0 
Alert Green  0.1
Alarm Dark Grey 0.2
Toxic Blue 0.5

The Ammonia Alert, when used as directed,  does not allow you to accurately raise the ammonia level past 0.5 ppm. However, you can calibrate your Ammonia Alert by counting the number of drops of ammonia it takes to turn it to the "toxic" level.  (Unfortunately, the Ammonia Alert does not respond instantly, so this may be a somewhat tedious process.) Multiply the number of drops by two to get the number of drops it would take to achieve a 1.0 ppm level and multiply times four to get the number of drops it takes to achieve a 2.0 ppm level. Keep in mind that due to the different net volumes in different tanks, this number of drops might be different for each tank you own.

3. Russell Taylor and Greg Tong experimented with the method and found that with tank water with low alkalinity2, the addition of even these small amounts of household ammonia caused pH spikes that retarded the growth of the bacteria. Since my own water is hard, alkaline, and of a high alkalinity, I did not have the problem. There are some websites that state that the pH of household ammonia is in the neighborhood of 11 to 12, which is quite alkaline. Hopefully, a good buffering product (say, Seachem's Neutral Regulator, which is quite inexpensive3) would take care of the problem.  Some partial water changes after cycling would be gentle enough transition to get the tank back to the desired unbuffered state.

4. Timothy Hovanec's recent articles (see below) have pointed out that the common nitrifying bacteria in freshwater aquarium systems are NOT Nitrosomonas and Nitrobacter.  Johnson's article stated that the optimal growth temperature for Nitrosomonas and Nitrobacter was in the 80's and 90's (F) and Lawson's Fundamentals of Aquacultural Engineering confirmed this. However, not knowing the exact bacteria involved (and their exact temperature range) does not make a whole lot of practical difference: I obtained good results from turning up the heat, so empirical evidence (at least my empirical evidence) supports the notion of turning up the heat speeds up growth.

Also, the revelation that we are probably not dealing with Nitrobacter or Nitrosomonas throws some doubt on the efficacy of commercial bacterial starter cultures (Hagen Cycle, Fritz-zyme, etc.). However, it is possible that the companies involved are constantly reformulating their products or that their products are effective, whatever bacteria they happen to be using. Keep in mind that if you do choose to use one of these products, you are probably not doing much  harm to the process: in view of the fish that you will not lose due to your cycling efforts, the cost of the products is minimal.


The method remains viable.  I don't see any reason for people to NOT use the method if they take the proper precautions. After looking at the newer material,  I don't see any reason to change the basic procedure, either. What should be added is a warning to buffer your water if you have low buffering capacity (you probably should be doing this anyway, then?) and to aim for a target level of 1-2 ppM ammonia while cycling.

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James S. Koga 
Major: September 2003
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In case you are not familiar with the nitrogen cycle, here is an excellent explanation:

Here are some links to pages that deal with the method: A related alternative method: mass seeding of a biofilter (but this requires you to have a large active biofilter on tap):

Some supplementary pages about Household Ammonia:

Bibliography Update:

Meyer, Stephen M. February 1999. Cycling Fishless [Ponds and Pondfish Column] . Aquarium Fish Magazine, 11 (2):81.

Hovanec, Timothy A.  March 1997. Nitrifying Bacteria [part 1] Aquarium Fish Magazine, 8 (3):44-52.

Hovanec, Timothy A.  April 1997. Nitrifying Bacteria [part 2] Aquarium Fish Magazine, 8 (4):32-43.

Hovanec, Timothy A. and Edward F. DeLong. August 1996. Comparative Analysis of Nitrifying Bacteria Associated with Freshwater and Marine AquariaApplied and Environmental Microbiology 62(8):2888-2896.


1  Or: How to use Household Ammonia to Split an Infinitive.

2  The water chemistry definition of "alkalinity" is not, as one might assume, how basic the solution is, but how much it resists changes in pH, which is the same as its "buffering capacity".

3 And, by the way, I failed to mention in the article that I habitually use this product in my tanks, though I don't think it made any difference in terms of pH spikes, given my water conditions.

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