How to Cycle Aquaponics

Starting Up (Cycling) Your Aquaponics System

 This article was borrowed from our friends at The Aquaponics Source

Bacteria are the carburetor of an aquaponics system that takes the otherwise unusable fish waste and creates a near perfect plant fertilizer. In this article I will demystify the process of establishing a beneficial bacteria colony in your aquaponics system. This process is often called system “cycling”. By the end of this article you will fully understand what you MUST do to initiate cycling and to ensure its success. You will also understand what you CAN do to both make the process less stressful for your fish and your plants, and to speed up the process.

What is Cycling?

Cycling starts when you (or your fish) first add ammonia to your aquaponics system. Ammonia (chemical formula NH3) is a compound made of nitrogen and hydrogen. It can come either from your fish or from other sources. Ammonia is toxic to fish and will soon kill them unless it is either diluted to a non-toxic level or converted into a less toxic form of nitrogen. In addition, nitrogen in the ammonia form is not readily taken up by plants, so no matter how high the ammonia levels get in your fish tank; your plants will not be getting much nutrition from it.
The good news is that ammonia attracts nitrosomonas, the first of the two nitrifying bacteria that are present in the air and will populate the surfaces of your system. The nitrosomonas bacteria convert the ammonia into nitrites (NO2) (the golden line in the chart above). This is a necessary step in the cycling process; however, nitrites are even more toxic than ammonia! But there is good news because the presence of nitrites attracts the bacteria we are truly after – nitrobacter. Nitrospira convert the nitrites into nitrates (represented by the green line in the chart above), which are generally harmless to the fish and excellent food for your plants.
Once you detect nitrates in your water and the ammonia and nitrite concentrations have both dropped to .5 ppm or lower, your system will be fully cycled and aquaponics will have officially begun!

The Importance of Testing Tools

API Freshwater Master Test Kit

You must have some way of telling where you are in the cycling process – typically a four to six week endeavor. Specifically, you must monitor ammonia, nitrite, and nitrate levels as well as pH so that you know that all these elements are “in range”. If they are not, you may need to take corrective action. This is also the only way that you will know when you are fully cycled and ready to add your fish. Plus, watching the daily progress of the cycling process is fascinating and something you can only see through the lens of a test kit. By the way, once you reach the point that your system is fully cycled, you will need to do much less monitoring than during the cycling process. So get through the cycling process and look forward to reaping the fruits (… or should we say the fish) of your labor.
To do their testing, most aquaponic gardeners use a product by Aquarium Pharmaceuticals Inc. called the API Freshwater Master Test Kit. This kit is easy to use, is inexpensive, and is designed for monitoring the cycling process in fish systems.
You will also need a submersible thermometer to measure your water temperature. Temperature affects both the cycling rate and the health of your fish and plants once you are up and running. See more on this below.

Starting the Cycling Process

Once you have your aquaponics system set up and your test kit in hand all you need to do to start the cycling process is add a source of ammonia. Traditionally this has been by adding fish and letting their waste be the ammonia, but I’m not a big fan of using fish as an ammonia source. Instead I prefer a technique called “Fishless Cycling” where an external source of ammonia is added to your aquaponics system. Why is this?

Typical Nitrogen Cycle

First, both you and your fish will likely experience much less stress because you will not be trying to keep anybody alive during the process. Second, you can more precisely control how much ammonia is added to your system during the process. For example, if you see that your ammonia level is creeping up to 8 ppm, but no nitrites have shown up yet, just stop adding ammonia for a few days and let the bacteria catch up. You can’t do this with fish!

The practical result of this is that with Fishless Cycling you can fully stock your tank once cycling is complete, versus gradually increasing your stocking levels as is recommended when cycling with fish. This is especially beneficial to those who are growing aggressive or carnivorous fish because they are less likely to attack each other if they are all introduced to the tank at the same time.

Cycling Without Fish

There are several ways to add ammonia to your system, but honestly the best is to simply purchase our Cycling Kits.  They come in 3 sizes – Small (< 100 gallons), Medium (100 – 300 gallons) and Large (300 – 500 gallons).  They come with all the ammonia you will need to fully cycle the corresponding size tank, powdered seaweed to provide a rich supply of micronutrients to get your plants off to a great start, and detailed instructions.
With Fishless Cycling you can add safely fish to your aquaponics system after your ammonia and nitrite levels drop to zero, or close to it, and you have measurable levels of nitrates.  This tells you that both the ammonia converting bacteria (nitrosomonas) and the nitrate converting bacteria (nitrospira) have become fully established and are ready to efficiently process fish waste.

Speeding up Cycling

Unfortunately nitrifying bacteria are some of the slowest growing bacteria in nature, and the cycling process can take as long as six weeks. There are a few things you can do to speed up this process, however.
• Temperature – like most microorganisms, nitrifying bacteria multiply more quickly in warmer conditions. Their optimal temperature is between 77-86°F (25-30°C). At 64°F (18°C) their growth rates is decreased by 50%. At 46-50°F (8-10 °C) it decreases by 75%, and stops all together at 39°F (4°C). It will die off at or below 32°F (0°C) and at or above 120°F (49°C).
• pH – Bacteria prefer a pH range between 7 – 8. Use hydroponic pH up and down products to keep your pH in this range during cycling.
• Oxygen – Nitrifying bacteria are aerobic and will multiply much faster under highly oxygenated conditions. Even if you are cycling without fish be sure to have as much oxygen in your tank water as you would if the fish were there. Think of the bacteria as just another living organism that requires oxygen in your system.
• Adding bacteria – You can “jump start” the process by adding bacteria from an existing colony. Good sources of beneficial bacteria are ranked here, leading with the best (the lower you go on the list the more chance you have of introducing a disease into your system):

• Our Microbe Lift Nitrifying Bacteria product (included with the Cycling Kits)
• Media from an existing aquaponics system.
• Filter material (floss, sponge, biowheel, etc.) from an established, disease-free aquarium.
• Gravel from an established, disease-free tank (Many local pet and aquarium stores will give this away if asked.).
• Other ornaments (driftwood, rocks, etc.) from an established aquarium.
• Squeezings from a filter sponge (any pet and aquarium store should be willing to do this…).
• Rocks from a backyard pond with fish in it.
• Rocks from a river, lake or wild pond.

When to add plants

We recommend adding plants as soon as you have started the cycling process.  The reason for this is that it gives the plants some time to put down roots and establish themselves before the fish are introduced and nitrates need to be absorbed.

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Below Grade Tanks

An in ground tank has several advantages.

• The ground will tend to stabilize the temperature, 
• The system can be built lower and still rely on gravity
• Less exposure to sun

There are many ways to build an in ground tank.  Each method comes with its own pros and cons.
Here is the list of cons
 
     1.  Set a molded tank into the earth.
           a.   Cost per gallon is high
           b.   Shape and size is limited
           c.   Susceptible to buoyancy if the tank is drained.
     2.   Build a concrete or block tank below grade.
           a.   Very costly
     3.  Build a wood box with a liner and set it into the earth
           a.   Costly in both time and materials.
           b.   Wood will eventually fail to insects and rot
           c.   Attention must be paid to the inward forces of the water table and or the earth.
     4.  Set an IBC into the earth
           a.   Prone to UV deterioration
           b.   Attention must be paid to the inward forces of the water table and or the earth.
           c.   Susceptible to buoyancy if the tank is drained. 
     5.  Dig a hole and line it with pond liner.
           a.    Uneven sides
           b.   Attention must be paid to the inward forces of the water table and or the earth. 
           c.   Susceptible to buoyancy if the tank is drained. 

Building a concrete tank is costly and labor intense, but the longevity is unparalleled. If you are dealing with a high water table it may be your best choice. Here is a link to a discussion I was recently involved in which addresses water proofing concrete tanks.

A molded tank set into the earth has the greatest appeal to many.   It is by far the easiest method and molded tanks can be found at reasonable prices.  An old hot tub can be used if you are feeling thrifty.

My least favorite is #3 because wood to earth contact is never a good idea.
I can not think of any advantage that would compel me to choose this method.  

Setting an IBC into the earth will provide a uniform smooth non toxic tank.  Protecting it from UV is important, but manageable.   To provide side support and prevent caving when the tank is empty, the back fill must be tamped down and compacted or cement should be added to the back fill to ensure stability.

Using a pond liner in a carefully excavated hole has some interesting advantages.   Pond liner is not susceptible to UV and it can be made any shape and size you wish.   This is the method I would like to describe here.

For the cost of the liner, some concrete and the form boards this method is simple and affordable.

Dig the hole to your specifications.
Drop the liner in and fill with water.  
Let the excess liner lay on top of the earth.
Then build a form around the edge and on top the the excess liner.  Include any conduit and rebar you wish and pour a high strength concrete into the form. 
Next day remove the forms and enjoy.

If you are pouring a low edge of 6" or less, the forms can be built very simply by drilling holes through the wood and connecting them with a piece of baling wire inserted inside of a spacing tube as shown above.  The wire can be tied off with a nail.  The spacer will remain inside the concrete after the forms are removed. Other materials such as a piece of paving block or even small piece of wood can be laid at the bottom. 
Lay a piece of rebar on the wires and secure the top with a piece of wood.   Be gentle but work the air bubbles out by running a rod up and down along the inside of the form.  Knock on the form with a hammer to settle the mix.  If this is not done there will be voids along the edges.

The concrete edge can be made any height, color and width.   You can make it  a work of art or as simple as you wish.

Here is a link to concrete information.

The simple rule is
1 part Portland cement
2 parts water
3 parts clean sand
4 parts gravel

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