Fishless Cycling: An 8 Step Guide That Will Guarantee Success!

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Cycling a new saltwater aquarium is a requirement that every aquarist must go through to establish a healthy and stable aquatic environment. If you use RODI water, eliminate all chlorine and chloramines, add base rock at 1-2 Lbs per gal, add a prepared source of nitrifying bacteria, add ammonia as a food source, and test daily, you will cycle your new aquarium within a few days.

I’ve cycled countless tanks and while there is no one “correct” method, the following method has become my tried-and-true go to and works every time. If you carefully follow these 8-steps your chances of success are near 100%.


Start by using Reverse Osmosis Deionized (RODI) water to fill your aquarium (and for water changes). Trust me, after years of experience, I emphatically discourage anyone starting a saltwater aquarium from skipping this step.  Do some research and get a good multistage RODI system.  Once it’s up and running, test your water with a Total Dissolved Solids (TDS) meter and make sure you are producing 0 TDS water.  This will ensure that your water is free of impurities and contaminants that could negatively impact the cycling process. There are countless options for RODI systems, I’m using the Spectrapure MaxCap 180 Gallon per day 4 stage system.  It has been completely reliable for me and I’ve had it in continual use for over 10 years.


Chlorine and Chloramines are disinfectants added to municipal water systems that can harm your aquarium’s beneficial bacteria. I’ve been in this hobby for over 30 years. When we moved into our new home in PA, I downsized from a 300-gal massive reef aquarium, to a 90 gallon Fish Only With Live Rock (FOWLR) tank.  We also now have city water, which compared to well water should not be a problem – right?  Should be easy, after all, keeping and propagating live corals is the real challenge, a FOWLR tank is a piece of cake for an experienced Aquarist, right? – Wrong! 

I had the most difficult time cycling this tank primarily due to Chloramines. I was well aware that Chloramines were used in our municipal system.   I had my Spectrapure RODI system set up and making 0 TDS water, however, it’s important to note that most RODI systems will not remove chloramines from the water as they are designed, so I added a chloramine cartridge to one of the stages.  Turns out the chloramine cartridge was still not enough to remove all of the chloramine and I could not cycle the tank. 

There are many good conditioners out there if you want to condition a batch of RODI water to remove chlorine and chloramines, but I have a system that keeps RODI water “on tap”, see my post on “How to Build a No Maintenance Saltwater Aquarium” for more detail if you are interested.  Since my system automatically filters RODI water based on level control, I needed a different solution. 

Enter The Chloramines Monster!  I added this to the outlet of my RODI system, and my tank almost immediately cycled.  You don’t have to add a large expensive polishing filter like this, my point is that you need to ensure that all impurities including chlorine and chloramines are completely removed before making up saltwater.  In your area, a chlorine/chloramine cartridge in one of the stages of the RODI system may be enough, just keep this in mind.  Once this is done, mix your saltwater to 1.025 SG.


The substrate you place on the floor of your aquarium, and the base rock you add as an aquascape will act as a home to your biological filtration.  I like to use small crushed coral with a depth of about 2″, and clean base rock at a level of 1-2 Lbs. of aquarium volume.   Many fishless cycling instructions advise you to use live rock as a source of nitrifying bacteria.  The problem with this method is that along with the nitrifying bacteria, other unwanted hitchhikers may tag along.  While many of these hitchhikers are organisms that are beneficial to your system, some are not, so in my opinion, it’s not worth the risk. For me, I want to be the one who introduces anything into my display tank.   Use a good quality clean base rock.  There are many options available that are designed to stack together to build solid aquascape base.  I’ll follow up with an article on aquascaping techniques in the near future.


In the past, many of these sources of bacteria were considered by hobbyists to be like snake oil and were not effective.  However, in recent years, they have become accepted by the community, and have been significantly improved.  I’ve used several, and I am a complete believer in two of them.  Dr. Tim’s One and Only and Fritzyme Turbo Start 900.  Without a doubt, Fritzyme has been by far the best performer for me personally.  Very clear instructions, and extremely reliable.  You can’t go wrong with either, but my recommendation is to go with Fritzyme.


Add a commercially prepared ammonium chloride designed for cycling an aquarium to provide a food source for the beneficial bacteria. These products are readily available at most pet stores and online retailers. Follow the instructions carefully to avoid over-dosing the ammonia.  I personally use Dr. Tim’s ammonium chloride.  I’ve actually talked with Dr. Tim a few times over the phone, he’s a real microbiologist, very knowledgeable and a helpful guy!


Testing your water regularly using a high-quality test kit is essential during the cycling process. You should primarily monitor ammonia, nitrite, nitrate, and pH, to ensure that the aquarium is progressing through the cycle correctly.  I’ve use API’s master Test Kit for years and have been happy with it.

Take the time to study and understand the nitrogen cycle: This is a must for all aspiring aquarists.  During the cycling process, the aquarium will go through a series of chemical changes that are collectively known as the nitrogen cycle. The nitrifying bacteria  added in step 4 will convert ammonia into nitrite, and then into nitrate. Initially, you will see a spike in ammonia, followed by a spike in nitrite, and then a rise in less harmful nitrate levels. Over time, these levels will drop as the beneficial bacteria establish themselves in the aquarium.  You will need to perform periodic partial water changes to keep nitrates levels low.


The cycling process can take anywhere from a few days to a few weeks complete, depending on various factors such as the size of the aquarium, the quality of the base rock and sand, and the source of ammonia. Be patient and continue to monitor your water quality regularly. When ammonia and nitrites have dropped to zero, and your are starting to see Nitrates, do a 10% water change.

Add Fish! 

Once the cycle is complete, you can now begin to add fish and other aquatic life to the aquarium, following best practices for stocking levels and acclimation.

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