Support Tank > Aquaponic Cycle > Cycling Without Fish

Cycling Without Fish


In addition to your hardware, whether it’s an AquaSprouts Garden or any other aquaponic system, you’ll need some supplies for cycling. Fortunately, most of these supplies will continue to be useful throughout the life of your system, so nothing should go to waste!

  • Water test kits: We strongly recommend purchasing at least a minimal set of water testing kits. This includes tests for Ammonia, Nitrite, and Nitrate (often sold together), as well as pH. Optionally, you may find test kits for carbonate hardness (KH) and general hardness (GH) helpful, especially if you’re using dechlorinated tap water as your water source. If you don’t want to purchase your own test kits, be sure you have access to water testing. Many pet stores and aquarium supply shops will test your water for free or a nominal fee, but unless you live next door to one, it will likely be cheaper and easier in the long run to obtain test kits yourself, as you’ll be testing your water frequently during this early stage.


Consider checking reviews for test kit brands or asking knowledgeable staff at a specialty aquarium or aquaponics store, as not all test kits are created equal, and some have better standards of accuracy and quality control. It's also very important to read and follow the directions of any test kits carefully!

  • Water chemistry adjustment kit: While “chemistry” may sound complicated, in most cases, all you’ll need for this is a dechlorinator (if you’re using tap water), a source of carbonate buffering, and acid and base additives to manage pH. You’ll also need fish food or pure ammonia, depending on how you’ve decided to cycle your system.
  • Logbook: Keeping a log or spreadsheet of test results and additions or changes can be extremely helpful in diagnosing problems or repeating the process if you do it again in the future.
  • Water: You’ll need to top off your tank to replace water which evaporates out, and eventually even the best-balanced aquaponic system may need a water change to remove accumulated salts or manage a fish health emergency. For top-off water, it’s best to use RO/DI (reverse osmosis/deionization) purified water, because it’s certain to be free of contaminants, and won’t add any extra salts or carbonates to your water. RO/DI water is often available by the gallon at aquarium shops or at water kiosks at grocery stores. If you can’t find RO/DI water, bottled spring water is also a good alternative as long as you check with other aquarists and aquafarmers to make sure the brand is safe. You can use tap water, as long as you use a dechlorinator, but this may make tracking your water chemistry more complicated, and in many places tap water will contain dissolved minerals and salts that will make it poorly suited to aquaponics.


Important note: For this guide, we’ll be providing instructions for fishless cycling, which we recommend. If you're cycling with fish, check out the supplemental guide  on our blog.

Before you begin cycling, set up everything the way it’s going to be set up during normal operation - that includes heaters, aeration, grow beds, media, pumps, and all the rest. You can also add plants at this point, though growth will probably be slow initially. Let the tank run for a day to make sure everything is working mechanically and let water temperature and chemistry normalize.

The most common varieties of nitrifying bacteria - the workhorses of your aquaponic system - like warm water, and since most aquaponic systems also house warm-water fish, you’ll want to keep your water temperature somewhere around 80°F. They also require water that's not too acidic, so when you first fill your tank, you’ll be keeping the pH and carbonate hardness (KH) higher than you usually would in an aquaponic system. Normally, you’d want to keep KH very low, since it buffers your pH upward - that is, it acts as a sink for the extra H+ ions which would normally make your water acidic. In this case, it’s okay to start with water with a KH of up to 30-40 mg/L CaCO3 and a pH as high as 8, though you'll still want to keep your General Hardness (GH) low.

AquaScience: As your nitrifying bacteria grow and oxidize ammonia and nitrite, they’ll produce extra free hydrogen nuclei (H+) which will react with water molecules to form hydronium (H3O+) ions. These will interact with carbonates in the water, which form temporary bonds and neutralize the extra positive charge, keeping your pH stable. As more ammonia and nitrite are metabolized, more H+ will be released into the water. If there are more hydronium ions than the available carbonates can neutralize, the water will acidify. This process will continue throughout the life of your tank, which is why pH tends to drift downward over time and can "crash" into a dangerous highly acidic state if not maintained. This can happen very quickly in small systems and is one of the primary long-term challenges faced by aquaponic growers! It's also why we chose a special growing medium for the AquaSprouts Garden.

If you’re starting with purified water, you’ll need to add some minerals to it, since all the living things in your system will need more than just ammonia to grow. Adjust the pH and KH with carbonate supplements until your pH is at least 7.2. You may also wish to add trace mineral supplements if you're adding plants at this point.

Your primary goal during cycling is to "feed" ammonia (NH3) to your growing microbial colony until they begin metabolizing it into nitrite (NO2) and then nitrate (NO3). This will happen in two distinct steps, since the second nitrite-oxidizing stage is dependent on the first for its nitrite "food" and can't start growing until there's oxidation of ammonia taking place.

This may take anywhere from a few days to a few weeks; it will take longer at lower temperatures and lower oxygen levels. You can help it get started much faster if you seed your system with bacteria-rich media or dirty water from an aquarium or aquaponic system that’s already cycled.

So, how much ammonia do you add? A good general target level for ammonia during cycling is 4-5 ppm (in most cases, for aquarium chemicals ppm and mg/L are roughly equivalent and used interchangeably, so you may see this written as 4-5 mg/L). This approximates the amount of waste produced daily in a moderately stocked aquarium.

Warning! Ammonia is quite toxic to aquatic organisms! You should never add ammonia to a tank with fish in it, or allow ammonia to reach the levels used in fishless cycling when there are fish in the tank. If you’re cycling with fish, the process will be quite different. Check out the supplemental guide! To calculate how much ammonia you need to add, give our ammonia dosing guide  a read.

After anywhere from a few days two a couple of weeks, you’ll start to see detectable levels of nitrite in the system. You can begin testing for nitrite at any time, but chances are you won’t see it right away unless you seeded your tank from an existing system. Keep adding ammonia and monitoring/adjusting pH, and after another week, start testing for nitrate as well.

After another period of waiting, typically 1-3 weeks, you’ll finally start to detect the presence of nitrate. Almost there! Nitrates are the end product of nitrification; they’re safe for fish at concentrations much higher than ammonia or nitrite, and they’re much more available to plants. However, at this point, the microbes which oxidize nitrite into nitrate have just gotten started, and they’ll need a little longer to establish themselves. Resume testing ammonia, nitrite, and nitrate every day, and keep adding ammonia and adjusting the pH. (Be sure to leave at least a few hours between adding ammonia and testing so the water has time to turn over and let the microbes do their work.) Soon, you should start to see your nitrates steadily increasing, while detectable ammonia and nitrite drop to zero. This means your biofilter is well populated - the bacteria are eating up those nitrogenous wastes as quickly as they’re introduced.

Technically, as soon as you can add a full dose of ammonia and test zero ammonia and nitrite 24 hours later, you’re ready to go, but it's a good idea to continue to dose ammonia and repeat the test for a few more days to be sure.

Once your biofilter is established, you can allow the pH to drop somewhat, into a mildly acidic range of pH 6.4-6.8 (acidic water makes many nutrients more available to plants) and get ready to add your fish and, if you haven't already, plant your grow beds! Wait between 12-24 hours after your last addition of ammonia and test to make sure it's all gone before adding fish.

Hit the ground running by adding your fish and starting your expected feeding regimen right away. Continue to test pH, ammonia, nitrite, and nitrate every day for at least another week, and be prepared to intervene with partial water changes or pH adjustments if your parameters fluctuate, especially if you see any ammonia or nitrite buildup. It’s a good idea to continue to check pH at least twice a week and ammonia, nitrite, and nitrate every 1-2 weeks for the life if your system. Check out the AquaSprouts blog for more detailed information on what different readings mean and how to deal with them, but here are a few common situations you may encounter after cycling is complete, and how to deal with them:​

  • Ammonia or nitrite is present: This means your biological load is exceeding the capacity of your biofilter. Either you’ve added too many fish too quickly, or you’re overfeeding them. Your biofilter may be able to catch up given time, but meanwhile, scale back your feeding and be prepared to do one or more partial water changes to remove excess ammonia from the system to protect the health of your fish.
  • No ammonia, nitrite, or nitrate is present: This indicates your plants are taking up nitrate as fast as your fish and biofilter can generate it. This isn’t a crisis situation, but it will slow down your plants’ growth and reduce your overall productivity. You can carefully increase your level of feeding or population of fish, a little at a time, until you can just barely start to detect nitrates, then back off very slightly, to reach a good point of balance between water that’s healthy for the fish and nutrient-rich enough for the plants.
  • Ammonia is present but nitrite and nitrate are not: When this happens, the first suspect is usually a low pH. Check it right away, and remember that your nitrifying bacteria need a pH that’s not too acidic to work. If your pH is below 6 and ammonia is present in the system, the ammonia may grab extra H+ ions from the water and become ammonium (NH4+) ion. This form is less toxic but it isn’t available to your biofilter! You’ll need to bring that pH up. Beware, however - as the pH rises, the ammonium will convert back to ammonia, so if you raise the pH too quickly, the sudden presence of concentrated ammonia may kill your fish! Try not to raise the pH by more than .2 per day if a great deal of ammonium is present. Keep a close eye on the system at this point - you may need to adjust it more than once per day until you get things back on track.