Fishless Cycling

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Swim with the Fishes
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Jan 18, 2005
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Mt. Holly, NC
Mod edit: This article has been superseded - please see this thread on fishless cycling.

There are threads almost daily about the proper method for fishless cycling. In actuality, a Google search will result in hundreds of links and each of those will give you slightly different instructions. I wanted to cover two of the most common ones and their advantages and disadvantages.

Let me start by saying that when you cycle a tank, you are really cycling the filter. That is where the vast majority of the nitrifying bacteria will colonize. Some bacteria are present on the tank walls, decorations, and in the substrate but for the most part they are in/on the filter. Basically, there are NO nitrifying bacteria present in the water itself.

First, a couple things that are common regardless of which method you use. Obviously, you set up the tank with clean, dechlorinated water. I believe it is best to fill the tank and let any sand/gravel dust or cloudiness settle for a few days before you add ammonia. This will prevent cloudy water from giving you a skewed reading when you test. Second, raise the water temperature to the mid to upper 80s. I have even had success with temperatures in the low 90s. The warmer water promotes bacteria growth and will speed the cycle. Also, you will need to add extra aeration via an air stone and air pump. The warmer water temperature will force the oxygen from the water so you must add aeration to replenish it.

Items Needed:

Bottle of pure ammonia. If you don't know where to find it, this thread may help you. Pure ammonia will only list ammonia and water as ingredients. Chelating agents are ok. Without going into great detail, that is simply a bonding agent that keeps the ammonia and water "mixed". If it lists dyes, fragrances or surfactants, you don't want it. If the bottle doesn't have an ingredient label, shake the bottle. If it foams, it won't work. A few air bubbles that disappear immediately are ok.
A good test master test kit. Get a good liquid master test kit. Those generally contain tests for ammonia, nitrite, nitrate, pH and high pH. You won't necessarily need the pH tests during the cycling process but you will later. I would also suggest getting a KH test kit too although, once again, it's not necessary for the cycling process.
A medicine dropper. Any cheap one that you get at the local drug store will do.

While you are waiting on the dust to settle and the water to clear, I suggest you do a couple things. First, test the parameters of your tap water. It is important to know the pH and KH of your tap water so you will know what fish are compatible with your pH. It is also very important to know if there is any ammonia, nitrite and nitrate in your tap water. A lot of municipal water supplies have some or all of those present and well water could also have them present. Knowing that could save you a lot of head scratching later when you have an elevated level that may be caused by your tap water rather than a problem in the tank.

You should also run a little test to determine how much ammonia to add to your tank. Since medicine droppers come in all different sizes, it's hard to say that you need X drops per gallon to get to 4 or 5 ppm to start. I have 3 different droppers for adding fertilizers and for drawing tank water for testing and there is a big difference in the size drops they dispense. Take a small bucket, one of the buckets you used to fill your tank or wash you're sand. Fill it with water and then add 2 to 4 drops of ammonia per 5 gallon of water. Swirl it around to mix it and test to see what the ammonia reading is. Continue to do this until your reading is 4 or 5 ppm. Remember how many drops of ammonia you added and then, some simple maths will tell you how much to add to your tank to get the 4 or 5 ppm required to begin cycling. You can also use a test tube to add it. The amount required will depend on the concentration of the ammonia but 1ml (about 1/5th US teaspoonful) will usually raise 5 gallon to about 5ppm.

Ok. Your tank is set up, the water has cleared, and you know how much ammonia to add. Let's get started.

"Add and Wait" Method

This is the method I have used to cycle 5 tanks (from 2.5 to 75 gallon) and it has worked perfectly. I think it is the simplest and requires the least amount of work. First add your ammonia to raise the level to 4 to 5 ppm (see ammonia calculator here at bottom of page). Now you simply wait on the ammonia to drop back to around 1 ppm. Spend the time researching the fish you like and see if they are compatible with each other, with your tap pH, tank size, etc.

Test daily to see what the ammonia reading is. There is no use to test for anything else. Nitrite and nitrate won't be present until some ammonia has processed. Ammonia will raise your pH so no use to test it either. Once you see a drop in the ammonia, test for nitrite. There should be some present. When the ammonia drops back to about near zero (usually takes about a week), add enough to raise it back to about 3 to 4 ppm and begin testing the nitrite daily.

Every time the ammonia drops back to zero, raise it back up to 3 to 4 ppm and continue to check nitrites. The nitrite reading will go off the chart. NOTE FOR API TEST KIT USERS: When you add the drops, if they immediately turn purple in the bottom of the tube, your nitrites are off the chart high. You do not need to shake the tube and wait 5 minutes. If you do, the color will turn green as the nitrites are so high that there isn't a color to measure them with. Once the ammonia is dropping from around 4 ppm back to zero in 12 hours or less you have sufficient bacteria to handle the ammonia your fish load produces. Continue to add ammonia daily as you must feed the bacteria that have formed or they will begin to die off.

The nitrite spike will generally take about twice as long to drop to zero as did the ammonia spike. The reason for this is two-fold. First, the nitrite processing bacteria just develop slower than those that process ammonia. Second, you are adding more nitrite daily (every time you add ammonia, it is transformed into nitrite raising the level a little more) as opposed to the ammonia, which you only add once at the start and then waited on it to drop to zero. During this time, you should occasionally test for nitrate too. The presence of nitrate means that nitrite is being processed, completing the nitrogen cycle. The nitrate level will also go off the chart but you will take care of that with a large water change later. It will seem like forever before the nitrite finally falls back to zero but eventually, almost overnight, it will drop and you can celebrate. You are almost there. Once the bacteria are able to process 4 or 5 ppm of ammonia back to zero ammonia and nitrite in about 10 to 12 hours. You are officially cycled. You can continue this for a few days just to make sure it isn't a one time thing and of course, you need to continue to add ammonia up until the day before you get your fish.

At this point, your tank will probably look terrible with brown algae everywhere and probably cloudy water. As I mentioned, the nitrate reading will also be off the chart. Nitrates can only be removed with water changes. Do a large water change, 75 to 90 percent, turn the heat down to the level the fish you have decided on will need, and you are ready to add your fish. You can safely add your full fish load as your tank will have enough bacteria built up to handle any waste they can produce.

"Add Daily" Method

I call this the "Add Daily" method because that is what you do. The start is exactly like the other method. To begin, you add enough ammonia to raise the level to 4 or 5 ppm (see ammonia calculator here at bottom of page). The difference is that the next day and each day thereafter you add the same amount. This continues until the ammonia drops to zero. This will take much longer than the other method because of the massive amount of ammonia the tank will initially contain. It generally takes about 3 days before any bacteria begin to form and you are able to notice even a small change in the color of your tests. In the other method, on the 3rd day there will still only be about 4 or 5 ppm of ammonia in the tank. With the "Add Daily" method, there will be approximately 12 to 15 ppm on the 3rd day so you need a lot of bacteria to process all of that.

Once the ammonia finally drops back to near zero, cut the amount of ammonia you are adding daily in half. That will still be plenty to keep the bacteria already developed fed. Continue to add the ammonia daily and test for nitrites. Once the nitrite drops back to zero, do your big water change and add your fish.

Advantages & Disadvantages: As I mentioned, the cycling process will take longer using the "Add Daily" method simply because you are forcing the bacteria to process quite a bit more ammonia. The advantage of that method though is that there will be much more bacteria present at the end than in the "Add & Wait" method. If you plan to have a heavy fish load (overstock) or keep messy fish (plecos, goldfish and Oscars for example), this may be the best way for you to go.

If you plan to keep normal tropicals with normal stocking levels as I do, cycling with the "Add & Wait" method should work fine for you. It has worked well for me. Some articles I have read even stated that if the ammonia level ever goes over 6 to 8 ppm that it severely slows the process and is a waste of time and effort.

Summation: As I said to begin, these are only 2 versions of the fishless cycle. There are numerous variations on these methods. One way to speed the cycling process is to "seed" the tank with a bacteria source from an established tank. See if a friend can give you an old filter from one of their tanks or if the local fish store has some gravel, filter media or anything that will provide a bacteria source. Any bacteria source will help.

As a general rule, don't waste your time or money on "bacteria starter" products such as Cycle or Prime. The consensus is that they serve no useful purpose. The fact that they have been shipped on un-refrigerated trucks and stored in hot warehouses leads most to believe that there couldn't possibly be any live bacteria left in the bottles. One possible exception is Bio Spira. I have personally not used this product but most things I have read suggest it works IF it has been handled properly (always refrigerated). Only purchase it from a reputable source that you trust.

Regardless of which method you choose, please, for the sake of your fish, do a fishless cycle. It prevents them from having to go through all the toxins and saves you a LOT of water changes, stress and lost fish. A little patience in the beginning will pay big dividends down the road.

Edit: I said that there was no use to test the pH as it didn't matter but after more reading, I have found that isn't entirely true. The optimal pH range for nitrification is about 7.0 to 8.0. As pH gets lower and closer to 6.0, the nitrification process severely slows. Below 6.0, the bacteria basically go dormant and stop reproducing. The bacteria that are present will continue to process ammonia and nitrite but the size of the colony will not grow or will grow very slowly. So in actuality, you do need to test pH to make sure it isn't too low.

Edit 2: There have been questions about high nitrate levels. While nitrate is indeed harmful to fish, that is only at very high levels, nothing our test kits will measure. Once the fish are in the tank, you want to keep the nitrate level as low as possible but that isn't as much for the fish as it is to prevent other issues such as algae. Once the fishless cycle is complete, the nitrate level will probably be 200 ppm or higher but a large 90% water change will take care of that. Try to lower the level to no more than about 20 ppm above your tap water before adding fish and you will be fine.
This should be immediately pinned. It is among the best fishless cycling articles available on the web, as far as I'm concerned.
I'm flattered. Thanks very much. I started it a month or two ago and then kind of forgot about it. I just hope it clears up some confusion and can be of help to beginners.
Very good get it pinned.
yeah, great article. well written for beginners :)

i agree even thou i have already cycled a tank it gets very confusing when reading all the different ways, i've always gone for the add & wait method which i'm doing on 2 tanks now. 1 of which is only 11 days in & showing nitrites over 5ppm & the nitrates at about 20ppm so getting there nicely now.
thanks for clearing this up rdd :thumbs: :D
As a newbie I was quick to find out that fishless cycling was important, but was getting confused with all of the different sources of advice. I knew it was important because a high percentage of questions in the beginner section were replied to with "have you cycled the tank" (even if the question was about fish food LOL)

I have just read through the above methods and feel a lot clearer on the subject.. so i would agree with the comments above about making the post the starting point for all newbies and pinned at the top.

Although.. can i ask one daft question before i go ahead.. what exactly does the "ppm" stand for when you say 5ppm

Daft Squid
Although.. can i ask one daft question before i go ahead.. what exactly does the "ppm" stand for when you say 5ppm
ppm is "parts per million" which is the measure on most test kits.
Aha.. thanks .. sounds like homeopathy to me :crazy: :crazy: :lol: :lol: :lol:
Very clearly and well put!

I did the second method and didn't actually find it took me very long at all. Probably different for different tanks.
Very clearly and well put!

I did the second method and didn't actually find it took me very long at all. Probably different for different tanks.
Thanks. I think different tanks do cycle in different times just like big tanks are generally more stable than smaller ones. It seems that most people who post that their cycling has stalled happen to be using the "Add Daily" method and the high amount of ammonia being added causes problems. I just hope more people will see that it is possible to cycle without fish in a reasonable amount of time.
Excellent article *insert clapping smiley, can't be bothered to look for it*. However, I do disagree with the
It is important to know the pH and KH of your tap water so you will know what fish are compatible with your pH

Obviously not the first bit, although theres not a great deal of point in testing very much as there is no point messing around with it, it often does more harm than good. The second part, though, isn't really true. All fish can easily be adapted to your pH, unless you have something like a 5.0 pH where you might need a little more thought. Even so called 'delicate' fish like discus can happily live in most pH's. The only real (common) exceptions are things like Mbuna and similar cichlids, who need a high pH, and some low pH fish, but this is only really a problem when it comes to breeding and ammonia (ammonia is more toxic in higher pH's.)
i wish i could of been able to read something like this when i first got my tank would of been very useful.
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