Calculating
Dissolved Oxygen Levels in Ponds & Lakes
Understanding the rate of oxygen transfer a diffuser can deliver
Whenever
the question of installing an aeration system comes up I am inevitably
asked how much oxygen will be delivered by the aerator. Of course
this is a standard question because the amount of oxygen being delivered
in to the water is critical if there are fish in the pond or if it
is an aquaculture system with a certain number of pounds of fish per
tank or per square meter.
Each diffuser has a different transfer of oxygen level and if we are
installing diffuser discs with medium sized bubbles or are using airstones
with micro-bubble sizes that are less that 1 mm per bubble then it
can make a huge difference.
Dissolved
Oxygen Meters
Using a dissolved oxygen meter is the most accurate way to ensure
your pond is getting the oxygen it requires to remain healthy.

Extech
407510 Dissolved Oxygen Meter

Dual display provides O2 or dissolved oxygen
and temperature readings Measures dissolved oxygen in
water from 0 to 20.00mg/L and oxygen in air from 0 to
100% Resolution: 0.1mg/L DO, 0.1% O2 Automatic temperature
compensation Min/Max/Average record/recall |
 Dissolved
Oxygen DO Meter Kit By Sper Scientific

.O., ppm and mg/L: 0~19.99 Resolution: 0.01 Accuracy:
±1.5% F.S.
Automatic temperature compensation 5 YR Warranty |
 Oakton
Dissolved Oxygen 110 Meter, with Probe

Stores and recalls up 100 dissolved oxygen (DO)
readings with corresponding temperature for reliability
during field use Water-resistant keypad for meter protection
Dual-line, LCD display of mg/L (ppm) or % saturation,
plus temperature in C or F. |
|
Let's take an example that even my Uncle Jimmy could understand: Jimmy
has a 4 acre pond and is thinking of adding a 3/4 HP rotary vane compressor
with 4 airstone diffusers and I think that it would likely be fine
considering he has a few deep sections near the dam that are at least
8 feet deep.
If his pond water has an average temperature of 68 degrees Fahrenheit
or 20 degrees Celsius and his levels have been measured by his Dissolved
Oxygen Meter to be 5 mg/l (5 milligrams per liter) then an aerator
that is rated at 3 pounds of raw oxygen per hour will really only
provide less that 1.3 pounds per hour (3 lbs x 41 percent = 1.23 pounds
of oxygen per hour).
I have to say to Jimmy: "I'm no scientist but let's put this
formula in the form of a chart so you can dwell and swell over the
numbers! No Jimmy...I ain't calling you out...but if you can understand
this chart then I owe you fifty bucks!"
For the creatures
of the Earth that inhale and breathe air a level of oxygen that is
around 21 percent is required to support life but in ponds, lakes
and aquaculture waters aquatic life is often supported in water that
contains less than 0.0001 percent oxygen, which is equal to 10 mg/l.
With such a small amount available in even the best of aquatic ecosystems
it is understandable why every aquculturist, serious koi or gold fish
owner, or even anyone interested in maintaining a fish pond or a healthy
water body should understand, measure and record the various seasonal
changes of the dissolved oxygen to ensure fish health and pond clarity.
If the oxygen level is too low, get yourself a pond aerator if this
is the case, your fish may stop eating and become lethargic and will
expend extra and unavailable energy trying to find their food...but
at the same time if the oxygen levels are too high then it can also
be a catastrophic fish-kill. At both extremes there can be extreme
fish stress and even death to aquatic life if the O2 levels surpass
critical thresholds.
Using a dissolved oxygen meter will allow you to regulate and understand
how your pond is evolving and when changes need to be made to adjust
the pH, temperature or aeration efficiency of your system you will
be able to quickly react!
I always tell the municipal lake-managers, pond owners and the homeowner
associations that I work for that they must take ownership and responsibility
of their pond or lake. It is the same with the small backyard fishpond!
The daily 24-hour cycle, sometimes called the diurnal cycle, of oxygen
addition and reduction in a pond should be well understood because
as you probably already know there is a delicate and fragile balance
between the existing dissolved oxygen in any pond or lake or water-garden
versus the absolute rate of oxygen consumption and this fluctuating
level can be altered by the shifting algae growth cycles, temperatures
and even the prevailing wind directions! In your outdoor ponds there
will be lower dissolved oxygen levels in the height of the summer
months, during June, July & August especially because during the
warmer months the overall rate of oxygen consumption in the pond will
increase as temperature increases.
This is why the most important thing to monitor will be the oxygen
level. The combination of monitoring your oxygen as well as other
chemical and elemental parameters of your pond combined with accurate
record-keeping will provide extremely useful and predictive knowledge
for the years to come as you deal with changing environmental systems
and patterns.
If you want to really get technical then the bottom line is that it
takes way more than just bubbles to correctly aerate a pond or lake.
When the oxygen levels are low you should be able to expect a transfer
performance of up to 10 pounds of dissolved oxygen per HP per hour,
this is using the standard rate so coveted by engineers!
Most pumps, water moving fountains and air bubblers are actually rated
at less than 2 pounds per horse power per hour. But as we have found
these ratings are often inaccurate because most O2 transfer happens
at the surface and not in the mechanical mixing or aerating.
Bubbles from diffusers tend to expand and spread out as they rise
from the bottom to the surface. The volcanic like mounting of water
that is pulled within the bubbles from one of our synergistic diffusers
rise at a rate that averages about one foot per second moving around
2,000 gallons per minute from the area above the diffuser assembly.
In comparison, a simple PVC pipe drilled with 1/64" holes will
only move 200 gallons per minute on average with the same 1/3 HP piston
compressor that delivers 3 CFM! Email
us with your questions
Know
your Dissolved Oxygen levels.
It really helps
Monitoring dissolved oxygen is a key to pond
& lake health
If you are considering one of the many commercially built pond
aerators then you will, if you are using a quality reviewed
system, be using one that has been evaluated and tested for
what is called the "Standard Oxygen Transfer Rate"
or SOTR which is the reliable measure of gaseous transfer that
is particularly useful for engineers and scientific types who
insist on understanding the minute details of how bubbles can
rise and conquer!
Understanding
Oxygen Transfer and Pumping Rates
Warning:
This next section is the kind of scientific, engineering talk
that makes most of my friends fall asleep in their bowl of chili...if
you continue beyond this point I am not responsible for any
of you who nod off and wake up tomorrow with your forehead stuck
to your computer keyboard!
If your water is literally "void" of any oxygen then
any sort of aerator, surface aerator, impeller system, bubbler
or bottom-mounted, lake-bed system will rapidly show performance
of adding dissolved oxygen at a rate that is typically 10 pounds
per horsepower per hour.
Many surface aerators provide excellent aeration and don't break
the thermocline which can be a problem in certain ponds and
lakes and such surface aerators are typically rated at closer
to 2 to 3 pounds of oxygen per horsepower per hour. I am sometimes
asked why are there these difference and these discrepancies
in data?
Mainly it is because advertised and stated SOTR rates are based
on waters that are deliberately as close to eutrophic or 0m/per
liter as possible thus making the device seem extremely effective
at providing the most pounds of oxygen per hour per kilowatt
or HP.
Despite the rated SOTR of any system it is rare that the maximum
rate will be achieved because the rate of O2 transfer is extremely
temperature and concentration dependent. What does this mean?
It basically states that any aeration system will only be able
to deliver the measured advertised maximum oxygen level when
the baseline levels are close to zero. It is rare that any body
of water will have D.O. levels approaching zero so often the
listed parameters can be erroneous. The following chart can
help estimate the oxygen transfer that your aerator will provide.
Oxygen
Transfer Rate (OTR)
As a % of the Maximum Listed Transfer Rate of Your Aeration
Device. |
Initial
Dissolved Oxygen Level
|
10°C
(50°F)
|
15°C
(590°F)
|
20°C
(68°F)
|
25°C
(77°F)
|
30°C
(86°F)
|
0
|
89%
|
90%
|
91%
|
92%
|
96%
|
1
|
82%
|
82%
|
82%
|
82%
|
82%
|
2
|
75%
|
73%
|
72%
|
72%
|
67%
|
3
|
67%
|
64%
|
62%
|
58%
|
56%
|
4
|
58%
|
55%
|
51%
|
47%
|
44%
|
5
|
52%
|
46%
|
41%
|
35%
|
31%
|
6
|
41%
|
36%
|
30%
|
24%
|
17%
|
These
levels are approximate for fresh waters at sea level. SOTR (Standard
Oxygen Transfer Rate) are typically used to describe mechanical
aerators such as paddlewheels, surface aerators and sometimes
fountains. With bottom diffuser aeration this science is rarely
used as the majority of oxygen transfer happens at the surface/atmosphere
interface where the aerator boil pushes waters to the surface
where the oxygen transfer occurs; thus depth and temperature
and CFM of the system involved plays a major role making the
SOTR rate almost inappropriate for discussion.
Dissolved
Oxygen Meters
Using a dissolved oxygen meter is the most accurate way
to ensure your pond is getting the oxygen it requires
to remain healthy. |
Congratulations:
You made it through this section... which according to my wife
was dryer than an Arizona bullfrog on a July rock! |
For
efficient oxygen transfer use diffusers and airstones with high pumping
rates and small bubbles: See
Our Diffusers & Airstones
For more information on pond aeration visit the following ten pond
aeration websites. Please note that we are not specifically endorsing
any particular way of treating ponds or any particular business. Due
diligence in all things!
1. Water Quality - Calculating the percent saturation is another
way to analyze dissolved oxygen levels. Percent saturation is the
measured dissolved oxygen www.cotf.edu/ete/modules/waterq3/WQassess3f.html
2. Dissolved Oxygen and Water Quality - A good level of dissolved
oxygen Is essential for aquatic life. ... As dissolved oxygen levels
in water drop below 5.0 mg/l, aquatic life is put underwww.state.ky.us/nrepc/water/wcpdo.htm
3. Dissolved Oxygen and Nutrients - Key Findings Report - NREI
- Aquatic animals need dissolved oxygen to survive. If levels of dissolved
oxygen become too low, many types of fish and other animals could
www.mb.ec.gc.ca/nature/ecosystems/nrei-iern/dg00s06.en.html
4. Major Findings - Dissolved Oxygen - Northern River Basin
Study - Winter is a critical time for dissolved oxygen levels. ...
Dissolved oxygen levels rarely dip below the Alberta surface water
objective of 5 www3.gov.ab.ca/env/water/nrbs/sect3/sect38.html
5. Science Junction - Water What Ifs - Dissolved Oxygen Lessons
- Decreases in the dissolved oxygen levels can cause changes in the
... Dissolved oxygen levels change and vary according to the time
of day www.ncsu.edu/sciencejunction/depot/experiments/water/lessons/do/
6. Canadian Water Quality Guidelines for the Protection of
Aquatic - Dissolved oxygen levels in aquatic environments can. affect
the persistence and bioavailability of some. chemicals. For example,
the persistence in water of
ceqg-rcqe.ccme.ca/download/en/178/
7. Dissolved Oxygen Meters, Portable Meter - Cole-Parmer Catalog
- METTLER TOLEDO's Dissolved Oxygen Sensors to monitor your processes.-
Dissolved oxygen meters are analytical instruments that are used to
measure the amount of oxygen dissolved in a liquid sample.
www.coleparmer.com/Catalog/product_index.asp?cls=46612
8. Hanna Instruments Dissolved Oxygen Meters - Meters for Laboratories
· Meters for Schools & Colleges · Swimming Pools Spa's & Hot Tub Testing
... You are here: Hanna Catalogue > Dissolved Oxygen Meters
www.hannainst.co.uk/acatalog/Dissolved_Oxygen_Meters.html
9. Pond and water garden test kits, test ammonia, pH, nitrites
... - Pond Test Kits testing pH, Salt, Dissolved Oxygen, Ammonia,
Nitrites, Nitrates, & More ... They're made in the USA, Available
meters are oxygen meters - Dissolved oxygen concentration in ponds
fluctuates on a 24-hour basis. .... Dissolved oxygen can be monitored
using an electronic oxygen meter or chemical
www.pondsolutions.com/test-kits.htm
10. Pond Aeration For Healthy Koi Ponds - In smaller fish/
koi ponds aeration is usually achieved when water ... Although a bit
pricey, a dissolved oxygen meter is one of the best - Dissolved Oxygen
Meter - Waterproof pH tester - Salinity Meter ... The meter is extremely
easy to use; simply turn it on and dip into your Koi pond - Disolved
Oxygen Meter Dissolved oxygen metering is an important application
test if efficiently maintaining koi ponds where oxygen levels are
important to
www.pondbiz.com/home/pb1/smartlist_323/h2o_test_kits__meters.html
Compare
Pricing of Dissolved Oxygen Meters For Ponds and Lakes
When comparing oxygen it is a good idea to look for forums and reviews
that discuss the pros and cons of various battery operated and AC
supply dissolved oxygen meters and check to see if they include a
deep-water probe or any probe with a 6 to 12 foot cable or more.
Since the principals
of oxygen measurements are scientific and many companies offer products
that do basically the same thing to various degrees of efficiency
then it is up to us as consumers to use our due-diligence before buying
a oxygen meter or DO meter. To compare prices with our recommended
meters we have grouped some of the more popular scientific and hobby
dissolved-oxygen meters brands together for comparison with our own
most used systems.
HANNA OXY-CHECK
WATERPROOF DISSOLVED OXYGEN METER
Measurements
in the field can subject the instrumentation to the inclemency of
the weather. Cold, rain, snow, dust and humidity associated with use
in the field can cause condensation, which may damage the meter, rapidly
deteriorating its performance and life. HI 9147 is designed for outdoor
applications, especially wastewater treatment and fish farming. Quick
response through the galvanic D.O. probe. Backlit Display. Simple
on-site calibration requires no chemical solutions. HI9147 also supplies
the user with compensation (manual) of salinity and altitude factors
and automatically compensates for the temperature effect.
Range 0.0 to 50.0 mg/L (ppm) O2 0-600 % O2 -5.0 to 50.0°C Resolution
0.1 mg/L or 1% O2 0.1°C Precision +/- 1% of the reading O2 +/- 0.2°C
Typical EMC Deviation +/- 2% of the reading O2 +/- 1°C Temp. Compensation
Automatic from -5 to 50.0°C Calibration Manual in Air Probe (Fixed)
HI 76409/4 with 4m Cable or HI 76409/15 with 15m Cable Battery 1 x
9V, Ni-MH, Rechargeable Battery Life 200 Hours of continuous use (without
backlit) Auto-Shut Off After 6 Minutes of Non-Use Environment 0 to
50.0°C, RH 95% Max Dimensions 164 x 76 x 45 mm Weight 511 g HI 9147-04
is supplied complete with HI 76409/4 D.O. probe with 4 m cable, 5
spare membranes, 2 O-rings, protective cap, HI 7042S electrolyte solution
(30 ml), Protective Rubber Boot, Screwdriver, rechargeable 9 volt
battery and instruction manual in a rugged carrying case. .
Available
at:
http://www.dynamicaqua.com
9200 Dissolved Oxygen Meter IP67
The
Model 9200 is a fully specified unit combining ease of use and robust
construction. Utilising a Clark type polarographic membrane electrode
optimised for both speed of response and the ability to withstand
the rigours of portable use, dissolved oxygen measurements can be
made either as % saturation or as concentration in mg/L (ppm). The
DO2 sensor incorporates a precision temperature measuring device which
determines and displays the temperature of the analyte and automatically
corrects for the changes in membrane permeability and oxygen solubility
which occur with variations in temperature. Calibration is a simple
push-button operation carried out in the % saturation mode with clear
instructions given via the graphics display. The sensor measures the
partial pressure of oxygen and the reported results are influenced
by atmospheric pressure and depth, unless appropriate compensation
is made. The standard 9200 allows these values to be entered through
the menu options.
The 9200 is equally at home in the laboratory environment and is suitable
for B.O.D. (Biolchemical Oxygen Demand dtermination. The optional
B.O.D probe and associated components are designed to faciltate the
5 day B.O.D. test as defined in ISO 5815. The kit includes adaptors,
allowing use with the many B.O.D. bottle configurations commonly available.
High quality waterproof connectors (to IP67) allow rapid interchangeability
of electrodes, whilst maintaining waterproof integrity. The connector
incorporates a locking ring to guard against accidental disconnection
or ingress of moisture. Power is provided by 3AA size batteries giving
typically 100 hours of use. An operator selectable auto shut-off feature
ensures battery life is maximised. Automatic low battery warning is
given when remaining battery life is approximately 5 hours (@ 20°C).
.
Available
at:
http://www.hannainst.co.uk
Oakton
® Waterproof DO 300 Meter Stones
Dissolved
oxygen (DO) readings are displayed in mg/L, ppm, or % saturation simultaneously
with temperature values. Adjustable backlit display makes it easy
to view readings in low light levels. Calibrate at the independent
100% and 0% calibration points to achieve high accuracy over the entire
range. Increase reading accuracy by entering salinity and barometric
pressure—meters automatically calculate offset. Setup function displays
electrode slope, zero offset, and millivolt values. Real-time clock
stamps stored readings and calibration data with date and time, making
it ideal for Good Laboratory Practice (GLP) standards. Additional
features include selectable °C or °F temperature units, HOLD function,
ready indicator, and auto-off for battery conservation.
IP-67 waterproof and dustproof housings float Perfect for harsh, rugged
field conditions Memory stores 50 readings with corresponding temperatures
and time Galvanic probe allows you to take measurements immediately
Percent saturation resolution 0.1% Percent saturation accuracy ±1.5%
full scale Temp resolution 0.1°F 0.1°C Temp accuracy ±0.5°F ±0.3°C
Temp range 32.0 to 122.0°F 0 to 50°C Temp compensation automatic from
0 to 50°C Salinity compensation manual from 0.0 to 50.0 ppt, 0.1 ppt
resolution Barometric pressure compensation manual from 500 to 1499
mm Hg/ 66.6 to 199.9 kPa; 1 mm Hg/0.1 kPa resolution
Available at:
http://www.coleparmer.ca/
Techne
Range of DO2 Dissolved Oxygen Meters by Jenway
Model
970 is a low cost hand held unit that is rated IP65 for portable use.
The Model 9200 Dissolved Oxygen Meter is designed and constructed
to resist the harshest of field, laboratory and industrial environments.
The whole system is waterproof to IP67, and if dropped into water
will float. These products are ideal for on-site water quality measurement
in a multitude of customer applications.
The 9200 utilizes a Clark type polarographic membrane electrode optimized
for both speed of response and the ability to withstand the rigors
of portable use. The Model 9150 DO2 Meter is part of our Premier Portable
range. The Model 9150 Dissolved Oxygen Meter is designed and constructed
to resist the harshest of field, laboratory and industrial environments.
The whole system is waterproof to IP67, and if dropped into water
will float. These products are ideal for on-site water quality measurement
in a multitude of customer applications.
The Model 9500 DO2 Meter is a bench top laboratory Meter. The Model
9500 is a fully specified dissolved oxygen meter that includes full
support for the B.O.D 5-day test protocol. Powerful data logging capabilities
are included with the ability to store up to 250 results plus 20 B.O.D.
tests (up to 10 samples per test) either manually, at timed intervals
or alarmed events. Remote monitoring and data collection is facilitated
by the provision of both analogue and digital outputs and in the event
of power removal all user defined parameters are retained.
Available at: aeratorsaquatics4lakesnponds.com
Email us for information or with your questions.
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