Aeration is pivotal to the success of your pond. One could argue more important than filtration because fish will succumb faster without oxygen then they will in water with high ammonia or nitrite levels
The ultimate success of your filter is based on adequate oxygen levels in the water. The filters aerobic bacteria require oxygen to carry out the Nitrogen Cycle effectively
In a fish pond, just having a waterfall will likely not be enough to keep the water at peak oxygen saturation points at all times, and besides, backup aeration should be in place via a dedicated air compressor |
There are 2 main ways of getting O2 into the water. Water to air contact is one, the other is oxygenating plants
A given area of pond surface will absorb a certain amount of oxygen based upon air pressure, temperature and other factors [ie surface tension, other gases etc.]. A waterfall for example, will encourage oxygen into the water by not only the splash, but also by the waves created throughout the pond which increase its total surface area by up to 3 to 4 times
In addition, plants will also release oxygen into the water as a byproduct of photosynthesis. In simple terms these primary producers absorb CO2 and output O2. There is a major caveat however. because plants can't be relied upon to oxygenate your pond 24/7 as they they consume oxygen at night . So the irony of "oxygenating plants" [really a misnomer] is that if you have a lot, it's even more important to have a good aeration system in place to counteract their oxygen consumption during nightfall
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This bottom drain is affixed with a dome aerator. This both aerates and creates beneficial water currents. In smaller ponds aerated drains can hamper fish viewing and do require a compressor that can deliver a suitable volume at depth |
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By providing optimum aeration levels, the environment for your koi is one that will allow for good health and growth. It also creates currents which mix the water and exercise the fish. Additionally, it discourages algae by expelling Carbon Dioxide and preventing stagnation
Surface tension is also dramatically reduced thereby facilitating the absorption of oxygen through surface to air contact. The bottom line is that aeration, along with a good filter system, are both equally integral in providing a excellent environment for your fish
Never run your pond without an air system - besides all the benefits it is a great backup to your pond when your pump fails (note: not "if your pump fails")
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This Air Assembly (for an earthen pond) utilizes a large piece of flagstone to both anchor and prevent soil erosion and subsequent turbidity
With deep pond aeration, the airstone can actually float up if not anchored properly |
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All serious Koi keepers have a dedicated aeration system running in their ponds and often in the bio chambers of their filters. There are basically 4 ways to aerate, each with their advantages and disadvantages
Aquarium Air Pump:
You should always have one of these on hand, especially a battery operated unit which can work during power failures or if you are on the road . They are inexpensive, good for small ponds and great in emergencies. They have limited air output
Compressor:
These units are a worthwhile investment. They put out quite a bit of air with good pressure which means they can be used for deep water aeration [a bottom drain for example]. Most are diaphragm driven so eventually the rubber membrane stretches and or splits - reducing effective aeration depth. Diaphragms should be changed at most every 2 years
Air Blower:
Blowers provide the most volume of air and are great for aerating a lot of tanks. The downside is that they are expensive and can't pump to the depths of compressors. Mechanically, airblowers by design will last longer than diaphragm compressors as they are almost like air fans
Venturi:
Venturis are probably the most efficient form of aeration. They operate off of your existing pumps return utilizing a physics trick in which air is drawn in through an airline by the restriction of flowing water. [the venturi principle]. They are inexpensive and great to augment / backup your main aeration system. Remember, you still need to have a separate aeration system because when your pump fails, the venturi will cease functioning. Operational depth is limited by pump flow rate and restriction size
With airstones look for good diffusion of air because the smaller the bubbles created, the better the aerating effect. Aquacultural grade airstones are therefore preferred and speced at an amount of air they can diffuse per minute [C.F.M. rating]. For maximum efficiency, try to match this rating to your compressors output. ie 1.4 CFM delivered to 3 feet - use 4 x .50 cfm airstones [1.5 x 6"] |
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Battery Air Pump
for a small cost this can save your fish |
Compressors
a great investment
for your pond |
Venturi
Very efficient aeration at
only a slight head loss penalty |
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Aerators come with different output ratings
These are generally CFM, GPM or LPM. Respectively Cubic foot of air per minute, Gallons per minute and litres per minute
Mathematically 1 CFM = 7.49 GPM = 28.4 Litres per minute. So although a 50 LPM unit sounds like a lot, it actually outputs less air than a 2 CFM compressor
Every 27" of depth in your pond equates to 1 psi of back pressure. A unit capable of 3 psi pressure will be able to pump air down to 6'9" |
As already mentioned, Oxygen is key for the conversion of Ammonia to Nitrite. Ammonia, NH3 is oxidized to Nitrite, NO2. As you can see, this reaction requires 2 oxygen molecules as Hydrogen is replaced by Oxygen
In a pond with low oxygen levels it is obvious that this process is crippled
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In extreme cases of Low D.O. levels [anoxic], fish will begin to gasp at the surface. If not readily corrected, they will asphyxiate and die
In more subtle circumstances, Koi may start gasping near day break after a night of both fish and plants depleting the O2 in the pond or by tending to congregate near waterfalls
Using an oxygen meter [or O2 test kit] and a thermometer, you can calculate your saturation point with the chart [right]. 80-85% would be an acceptable minimum
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