Fishless cycling is an easy method of getting your new aquarium ready for the safe introduction of fish. It does this by preparing your filtration system to handle the toxins that your fish will excrete once introduced. An unprepared filter system would allow those toxins to build to harmful or even lethal levels.

When fishless cycling, you will be adding an ammonia source to an aquarium to simulate the ammonia additions that would normally come from the fish. Bacteria that you will sometimes see referred to as 'nitrifying bacteria' will use this ammonia for fuel and they will build in numbers to colonize your filtration system. These beneficial bacteria will convert both toxic ammonia and nitrite to much less harmful nitrate.

I wrote this article with the intention of giving you just enough information to fishless cycle successfully without overwhelming you with many scientific details. You can find plenty of information on the science behind fishless cycling in articles elsewhere. I refer to some of this information later. I have also included common questions and problem situations regarding fishless cycling that I have encountered over the years.

Advantages of fishless cycling over cycling with fish -or- Why should I bother with this?

The biggest advantage to fishless cycling is that you can safely stock the aquarium without subjecting your new fish to toxic levels of ammonia or nitrite. Elevated ammonia and nitrite levels are capable of doing long-term damage to fish. Even if the fish survive and seem to not be affected, some harm may have occurred. You may not see the effects right away, but the damage done to a fish can affect the long-term health of the fish and shorten its life.1 Chronic exposure to low ammonia levels can cause gill and kidney damage among other maladies.2 Fish differ in susceptibility to these toxins. Short-term exposure can affect some fish more than others. Any time you cycle with fish and subject them to elevated levels of ammonia or nitrite, you put the fish's long-term health at risk.3

Another advantage of fishless cycling is that you can add all of your fish at one time. This can be very beneficial when stocking with aggressive cichlids. Introducing potentially aggressive fish together allows all of them to stake out and claim a territory without having to challenge those that are already well established. The new fish will have been stressed already from transport and introduction to a new aquarium. Long term, unalleviated stress has been shown to negatively affect the health of certain fishes during transport. If the fish has to also deal with the harassment of established aquarium occupants, the physiological changes that occur during stress will continue and can threaten the fish's health and survival.4 Adding your fish all at once can also be beneficial if you're ordering from an online supplier, as you'll save on shipping costs and not have to deal with multiple shipments.

Myths about fishless cycling

Myth #1 -- Fishless cycling takes longer than cycling with fish.

In some cases, this could seem to be true. If you cycle with a few small fish that are excreting a minimal amount of ammonia, you will need to only build a small bacteria colony to handle that ammonia. This takes less time than building a bacteria colony that can handle a full load of fish. However, you would then proceed to slowly add additional fish and wait for the bacteria colony to increase enough to handle the additional load. You need to continue repeating this process of adding a few fish until the full stocking of the aquarium is complete. So, you may cycle more quickly initially, but the bacteria are only able to handle the initial small load of fish. To get the aquarium up to full load and capacity will take a few weeks, even when cycling with fish.

Myth #2 -- Fishless cycling is complicated.

I will hopefully dispel that myth below. Some methods I have seen are a bit complicated, very true, but unnecessarily and to no advantage, in my opinion.

Here is a quick summary of steps.

• Work out your formula for your initial ammonia dose and add that to the aquarium.
• Test for ammonia every 24 hours until you get a reading of zero.
• Add ammonia every other day while testing for nitrite. Do small partial water changes.
• When the nitrite test reads zero, do a series of small, partial water changes to bring nitrate down.
• Add the last dose of ammonia 48 hours before adding fish.

It is no more complicated than that.

Detailed steps to fishless cycle

--Get your aquarium set up, filled with water, filter(s) running, and water up to a temperature of about 85 degrees, as warmer temperatures can accelerate the growth and multiplication rate of nitrifying bacteria.5 Keep your aquarium lights off for now, as there's no reason to run up the electricity bill and encourage algae to get off to a good start before you even have fish in the aquarium. If you do decide to run the lights, don't worry about any haziness in the water during the cycling period. If you are intending to use power heads or other water movement pumps to circulate the aquarium water, get them in place and running because nitrifying bacteria may be inhibited by low oxygen levels in the water.5 Nitrifying bacteria need oxygen just like fish or other aquatic creatures. The circulation of the water will help to keep oxygen levels high.

--Test your water's pH and KH. It is best for cycling if pH is 7 or above and KH is at least 4 or 5. If your pH is low, (below 6) then the bacteria that are responsible for cycling an aquarium may be inhibited.5 If pH is fine, but KH is low, then the stability of your pH may be in jeopardy. A moderate KH level is needed to stabilize pH. Therefore, a pH of 7 today might be 6 or less tomorrow if KH is only 1-2. If your pH and KH levels are fine, then don't worry about making them ideal for your fish for now, just move on to the next step. You can fine tune water parameters later, if needed. (For more info on how to increase pH and KH, there are excellent articles in the forum library under the 'Chemistry' section titled 'Practical Water Chemistry' and 'Rift Lake Buffer Recipe'.)

--Add ammonia at the rate of 2 drops per gallon. Why add 2 drops per gallon? It is just a starting point, that's all. You can start with less if you like. Wait 20 minutes for the ammonia to circulate and fully mix into your aquarium water and then run the ammonia test. (If you are not sure what kind of ammonia to add, see 'What kind of ammonia should I use and where do I get it?' under 'Frequently Asked Questions' below.) You are aiming for an ammonia level that is somewhere between 1-2ppm. (See 'What does ppm mean?' below.) By the way, there are about 100 drops in a teaspoon. It may be easier to measure out your ammonia dose with a teaspoon rather than an eyedropper. In addition, keep in mind that hobbyist test kits are not precise and that is ok because you do not need a precise reading. If the ammonia level looks somewhat like it is in the proper range, then that is good enough. Those color cards that come in the test kits can be very tough to read.

If your ammonia level is low, then calculate how many more drops you need to add in order to raise it up into the desired range. For instance, if your ammonia level is now .5ppm, then add another 2 more drops per gallon. So for say a 20 gallon aquarium, add another 40 drops. Test again after 20 minutes to confirm that it is now in a good range. If it is still low, then add more while keeping track of the total amount of ammonia (drops, teaspoons) added.

If your ammonia level is too high, say 3-4ppm, that's ok. Just make a note that future doses only require half of your initial dose. So, your formula might be 2 drops for every two gallons instead of every gallon. You could always do a water change to bring the level down to 1-2ppm, but this is only necessary if you have overdosed to a level above 5ppm. A very high ammonia level will inhibit the nitrifying bacteria responsible for cycling.5

Be sure to make a note of the total drops/teaspoons added. You will need this information later.

--At about the same time each day test your aquarium water's ammonia level. Do not add more ammonia just yet. That comes in the next step. It will seem like the ammonia level is never going to drop, but it will, so be patient. It can take anywhere from 7-10 days, typically. You will not necessarily see a gradual decline, but more of a sudden drop. You may get a slight reading of .5 or so one day, and then get a zero reading the next. When you get a reading of zero, you are ready for the next step. Do not start adding more ammonia on the day that it starts to decline. It is not necessary. Wait for the test to indicate that it's zero. (I would suggest that if you are not familiar with the nitrogen cycle that you read the excellent article in the forum library under the 'Chemistry' section titled 'The Nitrogen Cycle'. It is not necessary to understand the details of the nitrogen cycle in order to fishless cycle, but you may find it helpful to understand something of the processes involved if questions or problems arise. So, while you are waiting for that ammonia to drop, take some time to check it out.)

--Now that ammonia reads zero after 24 hours, you will need the note that you made regarding your initial ammonia dose. However many drops/teaspoons you added initially, add that many again now. You will add this same dose every 2-3 days. Go for consistency, but it is ok if you forget or get busy and skip a day. It will not derail the processes that are happening. In addition, you do not have to add the dose at exactly the same time each day, but best to be somewhat consistent when adding and testing. Try to set aside a time each day for this.

--Now that you have built up enough bacteria to convert ammonia within 24 hours, you can stop testing for ammonia and begin testing for nitrite. The nitrite drop can take up to 2-3 times as long as the ammonia drop. This length of this phase can lead some to think that the cycle is not progressing. However, it is progressing, so be patient. You will probably get a nitrite reading that is very high, even off the chart. That is normal. In order to ensure that things speed along just as quickly as possible, you can perform partial water changes to keep the byproducts of nitrification down because just like excessive ammonia levels they will inhibit the nitrifying bacteria.5 You can perform these water changes daily. However, I would suggest not changing too much water at one time. Try 30% or so daily. (See why in 'Cautions, tips and tricks' below.)

Here is what your daily routine going forward will look like:

• Test for nitrite, perform water change, and then add ammonia.
• Next day; test for nitrite, perform water change.
• Next day; test for nitrite, perform water change, and then add ammonia.
• Next day; test for nitrite, perform water change.
• Next day; test for nitrite, perform water change, and then add ammonia.

The daily tests of nitrite will let you know the effect of the water changes on the nitrite level. You are looking for a zero reading, of course, but that can take a while. Only test for nitrite once per day, about the same time each day. Again, do not test any longer for ammonia. We can assume it will be zero each day now. Make an effort to keep nitrite down below 5ppm by way of small, partial water changes. The ammonia additions will ultimately raise the nitrite level while the water changes will drop it back down. Do not over analyze the test results. You are just looking to see if the water changes that you are performing are adequately keeping nitrite down. You are ultimately looking for a nitrite reading of zero.

--The next and final steps begin when you do finally get that nitrite reading of zero. Like ammonia, you will not see a gradual decline in the nitrite level, but instead you will see more of a sudden drop over a day or two.

--Now that nitrite is also being converted within 24 hours, it is time to start testing for nitrate. Notice that we have not done the nitrate test yet. Do not get tempted to test for nitrate sooner than this. Check out the section titled 'Testing for nitrate with nitrite present' under 'Cautions, tips, and tricks' below for more of an explanation.

--Perform a series of partial water changes over the next day or so in order to get nitrate down to 20ppm or so. Avoid the temptation to do one massive water change. Treat your new colony of bacteria like a delicate, fragile living thing. I have seen massive water changes on a newly cycled aquarium result in a temporary nitrite spike. It does not always happen, but why risk it? The last thing you want to see after finally getting a zero readings are small spikes. If they do happen, I have found that these spikes are small and brief, so no major harm done.

--Continue adding your ammonia dose every other day or so until you add your fish. Add the last dose of ammonia 48-72 hours before adding fish. This will give you time to do any final water changes to get nitrate levels down without fighting the addition of new nitrate resulting from the addition of more ammonia. This will also provide time to ensure that the filtration has fully converted all of the ammonia and nitrite into nitrate before adding fish.

--The last step is to add your fish.

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