If you have been following this series on how to build a media based
aquaponics system,
you now have your aquaponics fish tank and grow bed interconnected by
flood and drain plumbing which is ready to be powered by a pump. Your
grow bed is filled with the grow media and the fish tank is full of
de-chlorinated water. Now it’s time to move into the living elements of
your system, starting with establishing the nitrifying bacteria.
Bacteria are the magic that takes the unusable aquaponics fish waste
and creates a near perfect plant fertilizer. In this article and the
next, we will demystify the process of establishing a beneficial
bacteria colony in your
aquaponics system.
This process is often called system “cycling”. Today I’ll talk about
cycling using fish and next month I’ll go into how to cycle without
fish. By the end of these two articles, 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
system. Ammonia (chemical formula NH3) is a compound made of nitrogen
and hydrogen. It can come either from your fish or from other sources
that we will discuss next month. Ammonia is toxic to fish (more on this
later) and will soon kill them unless it is either diluted to a
non-toxic level or converted into a less toxic form of nitrogen.
Unfortunately, nitrogen as found in ammonia 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 will populate your system. The nitrosomonas
convert the ammonia into nitrites (NO2). 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 nitrospira. Nitrospira convert the nitrites
into nitrates, 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 or lower your system will be
fully cycled and aquaponics will have officially begun!
The Importance Of Testing Tools
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 more fish (or your first
fish if you have been cycling with no fish at all). 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.
Cycling with Fish
Ammonia (NH3) is the catalyst that starts the cycling process. You
must have some means to feed ammonia into the system so that you attract
the bacteria that are at the heart of aquaponics.
There are two ways to introduce ammonia into your system with fish
and without (fishless). Today we will talk about cycling with fish, and
tackle fish-less cycling in the next article.
The Ammonia (NH3)
I used fish to cycle my first
aquaponics system and
I suspect this is how most people approach cycling. In some ways it is
the easier of the two methods because there are no extra inputs, but it
is definitely the more stressful of the two options because live
critters are involved.
The idea is to add fish on day one and hope that they live through
the cycling process. The challenge is to get the system cycled fast
enough that the ammonia concentration from the fish waste drops to a
non-toxic level before the fish succumb to exposure to their own waste. I
strongly recommend that you don’t stock to your tank’s mature capacity
(1 lb of fish per 5 – 10 gallons of water) but to less than half that.
You might also want to consider these fish as “sacrificial” and perhaps
use goldfish from the pet store, which are fairly tolerant of ammonia,
rather than the tilapia with which you may ultimately envision stocking
your tank. Also, do not feed these fish more than once a day and only
feed them a small amount even then.
Fish excrete ammonia through their gills as a bi-product of their
respiratory process. Without dilution, removal or conversion to a less
toxic form of nitrogen, the ammonia will build up in the fish tank and
eventually kill the fish. In addition, ammonia (NH3) continually changes
to ammonium (NH4+) and vice versa, with the relative concentrations of
each depending on the water’s temperature and pH. Ammonia is extremely
toxic to fish; ammonium is relatively harmless. At higher temperatures
and pH, more of the nitrogen is in the toxic ammonia form than at lower
pH.
Standard test kits measure
total ammonia (ammonia plus ammonium) without distinguishing between
the two forms. The following chart gives the maximum long-term level of
ammonia in mg/L (ppm) that can be considered safe at a given temperature
and pH.
Water Temperature
| pH |
20C (68F) |
25C (77F) |
|
|
|
| 6.5 |
15.4 ppm |
11.1 ppm |
| 7.0 |
5.0 |
3.6 |
| 7.5 |
1.6 |
1.2 |
| 8.0 |
0.5 |
0.4 |
| 8.5 |
0.2 |
0.1 |
You will need to monitor your tank water daily during cycling for
elevated ammonia levels. If those levels exceed the levels on the chart
above you should dilute through a water exchange by pumping out up to
1/3 of your tank’s water and replacing it with fresh, de-chlorinated
water.
Adjusting pH
During cycling, especially with fish, you should try and keep your pH
between 6.0 and 7.0. The range does not go below 6.0 because most fish
prefer slightly alkaline water and few are happy below 6.0. The range
does not go above 7.0 because of the ammonia toxicity issue described
above (higher pH readings suggest higher ammonia concentrations). So how
do you keep pH in such a tight range?
The first rule is: Whatever you do to adjust pH in aquaponics – Do it
slowly! Fast, large pH swings are very stressful on fish and will be
much more of a problem than having pH that is out of range. Target
shifting your pH reading no more than .2 per day and you should be fine.
The safest way to do this is to use our
AquaDown pH Lowering Solution. Raise pH either by using our
AquaUp pH Raising Kit
or by alternating alternatively use calcium hydroxide – also known as
“hydrated lime” or “builder’s lime” with potassium carbonate (or
bicarbonate) or potassium hydroxide (“pearlash” or “potash”). Don’t use
citric acid as it is anti-bacterial!
Typically, you will be trying to keep pH down during cycling, and
then once your system is cycled you will probably notice that the pH
will fall and you will then need to switch to keeping it up. You will
probably find that it is easier to increase pH than it is to decrease
it. The ideal pH of a mature aquaponics system is 6.8 – 7.0. This is a
compromise between what the plants prefer, i.e. a slightly acidic
environment of 5.5 – 6.5, and what the fish prefer, i.e. a slightly
alkaline environment as we discussed before.
The Nitrite (NO2)
Nitrite is to fish like carbon monoxide is to air breathers. The
nitrite will bind with the blood in place of oxygen and keep the fish
from getting the oxygen it needs. Fish poisoned with nitrites die of
what is called “brown blood disease”. If the nitrite levels in your tank
rise above 10 ppm while you are cycling your system with fish, you
should do a water exchange as discussed above, but you may also want to
add salt to the system in order to further protect the health of the
fish.
Do this by adding
salt to
the system to at least 1 part per thousand (1 kg of salt per 1000
liters of water) using non-Iodized salt. Avoid table salt since it
contains potentially harmful anti-caking agents. You can use cheap pool
salt or water softener salt available at the grocery or hardware store,
but the best product is
salt specifically formulated for fish.
Make sure to dissolve it completely in a bucket of water before adding
it to the fish tank since un-dissolved salt crystals on the bottom of a
fish tank can burn a fish that rests against them. Stop feeding your
fish until the nitrite levels decline below 1.0 and aerate as much as
possible.
How might salt (sodium chloride) help? Sodium Chloride helps mitigate
nitrites because the chloride ions bind with the nitrites and thereby
help keep some of the nitrite out of your fish.
Adding Plants
I
recommend adding plants to your new aquaponic system as soon as you
start cycling. Plants can take up nitrogen in all stages of the cycling
process to varying degrees; from ammonia, nitrites and nitrates, but
they will be happiest when cycling is complete and the bacteria are
fully established because so many more nutrients become available at
this stage.
When plants are first transplanted, they focus on establishing their
root system in their new environment. You may initially see some signs
of stress – yellowing and/or dropped leaves – and you will probably not
see any new growth for a few weeks. This is fine. Adding plants to your
system right away lets them go through the rooting process early on and
readies them to start removing the nitrogen-based fish waste from your
aquaponics system as soon as possible.
I recommend you use some
Maxicrop
to get your plants off to a good start during cycling. Maxicrop is
derived from Norwegian seaweed, is organic and is used primarily as a
growth stimulant, especially to enhance plant root development. It is
extremely effective at giving plants a “leg up” after being transplanted
into your new aquaponics system, is absolutely harmless to the fish,
and probably beneficial for the bacteria. You can find Maxicrop in
garden centers, hydroponic stores, and online in both liquid and dry
form.
While there are no hard and fast rules about how much
Maxicrop to
add during cycling, I recommend about a quart of the liquid product for
every 250 gallons of water. It will turn your water almost black but
don’t worry; this will clear up after a week or so.
Speeding Up the Process
Cycling is in some sense akin to any hunting activity that uses a
lure. We start by putting out the ammonia. This attracts the
nitrosomonas bacteria which in-turn produces nitrites. The nitrites
attract the nitrosprira bacteria which produce the nitrates that are
harmless to the fish and delicious to the plants. These two beneficial
nitrifying bacteria are naturally present in the environment.
As I stated earlier, this process will take four to six weeks if done
with fish, or as little as ten days to three weeks if done fishless.
But what if you could speed that up significantly? What if instead of
waiting for the bacteria to show up to the party, they actually are part
of the party to begin with? You can do this by introducing nitrifying
bacteria into your aquaponics system.
Adding Bacteria
While there are many ways to do this, they all boil down to two basic
strategies: use bacteria from an existing aquaculture or aquaponics
operation or from a near-by pond or instead, purchase bacteria from a
commercial source.
Good sources of beneficial bacteria from existing systems are ranked here, leading with the best:
- Media from an existing aquaponics system
- Our Microbe-Lift Nitrifying Bacteria product
- 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 might be willing to do this…)
- Rocks from a backyard pond with fish in it
Managing Water Temperature
Water temperature also has a dramatic effect on the speed of cycling.
Their optimal temperature is between 77-86° F (25-30°C). At 64°F (18°C)
their growth rates is decreased by 50%. At 46-50ºF (8-10°C) it
decreases by 75%, and stops all together at 39°F (4°C). It will die off
at or below 32ºF (0°C) and at or above 120°F (49°C).
Cycling with Fish – Conclusion
While cycling with fish is the most widespread and straightforward of
the cycling techniques, it is stressful on your fish and therefore
somewhat stressful for you. But it certainly works. Next month we’ll go
over another technique called Fishless cycling that uses pure ammonia to
cycle your system.
Either way, it’s time go get up and grow!
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