One of the things that confounds the beginning aquarist and those
not schooled in the science of chemistry is the problem of a falling pH that usually
occurs overnight. A change in Ph of 0.10 is considered a normal occurrence. It is normal
because as changes occur in the atmosphere and oceans, all living things have learned to
adapt to these changes. This article will deal with just one of the environmental
conditions that will affect pH. One of these is the increase of carbon dioxide in well
sealed homes that do not have a fresh air intake installed on the heating and air
conditioning systems. This compounded by the lack of an exhaust fan to pull out stale air.
I am also hoping to stir up some interest in Indoor Air Quality for all aquarist's who
have never given it a thought that their every day habits contribute to a downward trend
in water quality. Later in this article, I will give some web sites that you can download
information on indoor and outdoor air pollution. When a residence is not provided with
proper ventilation, an increase of CO2 will occur and this mostly happens at
night when all windows are secured and the occupants retire for the night. In the indoor
environment, the main contributors of C02 are human beings and the use of fuel
burning appliances. Human beings are responsible for most of it.
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The amount of C02
that it takes to lower pH is indicated in data presented below. The data will be
interesting to those who want to improve the air quality and to maintain a stable pH. The
outdoor C02 concentration is about 340 ppm. But the concentration indoors can
easily reach over 1200 ppm, which is enough to effect the pH downward 0.30 to 0.40. I
performed 3 tests to determine just how much C02 is needed to bring down pH,
when the alkalinity is 3.5 meq/L. Prior to my first test, I opened all the windows and
interior doors to balance the indoor concentration with the outdoor C02
concentration. I did this with the help of a carbon dioxide monitor that has a continuous
digital readout. I placed this monitor in the fish room. My presence in the fish room
added 40 ppm to the reading over outside air concentration when the test started. Here are
the results:
TEST #1:
Test start time
pH
CO2 concentration
Test end time
pH
CO2 concentration
8:00PM
8.34
380ppm
6:00AM
8.33
380ppm
As you see, with low C02 concentration, there
was only a 1/100 drop in pH.
In test #2, I balanced the air again. After which I then closed all
windows and two interior doors that lead to the fish room. The room is 13 by 15 by 7 feet
high. With no ventilation coming into the room and myself as the only occupant of the
house, I stayed in the room for 3-1/2 hours.
TEST #2:
Test start time
pH
CO2 concentration
Test interval
pH
CO2 concentration
8:00PM
8.38
400ppm
11:30PM
8.20
1020ppm
Test end time
pH
CO2 concentration
6:00AM
8.21
540ppm
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In this test, there was a
significant drop in pH of 0.18 with a high concentration of C02. If there was a
crowd of people in the room under the same test conditions, the decrease in pH would not
have taken 3-1/2 hours. Some aquarist's have already noticed this effect.
The final 6:00 am test readings indicate two
things: one is that the pH cannot recover as quickly as it dropped because, as is well
known by experienced aquarists, C02 can easily enter seawater but takes longer
to be blown off by aeration or water movement. And the other is that it took 6-1/2 hours
after opening the two interior doors to vent the excess C02 in the rest of the
house to bring it down to 540 ppm.
In test #3, 1 left the room immediately and
did not enter until the test was over. As in test #2 the air was balanced with the outdoor
concentration.
TEST #3:
Test start time
pH
CO2 concentration
Test end time
pH
CO2 concentration
8:00PM
8.37
410ppm
6:00AM
8.26
660ppm
As you see, this test indicates a normal drop in pH when
the C02 levels are kept in the range of 600 to 660 ppm. For economic reasons,
this is the range I keep during the heating and cooling seasons. At other times in the
year, my pH moves in a range of 0.05 because I usually have doors and windows opened. Now
the question of alkalinity comes up. I did not want to change it lower or higher as my
tank is running fine. But I believe that if the alkalinity was raised, then it would take
a higher concentration of C02 to effect the pH. So if you have a falling pH,
you can determine if excess C02 is the cause by following this procedure and
comparing your results with the difference between my starting pH and ending pH and its
final C02 concentration which should give you a better then ballpark figure for
your CO2 concentration. For instance, if your test procedure indicates a drop
of 0.10 pH, then looking at test #3 shows a drop of 0.11 with a ending concentration of
660 ppm. This would be your approximate C02 levels in the fish room. Here is
the test procedure you should follow:
In the
evening, take a sample gallon of tank water and with a strong aerator, place it in a
sheltered location outdoors -- this is important -- and let it aerate for at least 9
hours. But, make sure you take a pH reading the next morning, before the lights come on
and before too much sunlight has a chance to effect your readings on your sample gallon.
This is because algae will start photosynthesis when the test water is exposed to enough
light and this in turn will start to raise the sample water’s pH.
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To make it easier for you to interpret your test
reading, here are some numbers to go by:
At a difference in pH of 0.05 or less
C02 it is about 340 to 380 ppm
At a difference in pH of 0.10
C02 it is about 600 to 650 ppm
At a difference in pH of 0.20
C02 it is about 800 to 1000 ppm
At a difference in pH of 0.30
C02 it is about 1100 ppm or higher
Now that we see how C02 affects
the pH, what can you do to control it? As mentioned earlier, you have to install a fresh
air intake into your heating and air conditioning mechanism, and or add an exhaust fan or
open nearby windows.
For those of you who may be interested in the
instrument that was used to measure C02 concentrations, it is manufactured by
the "Vaisala" company, and to see the specifications and more information, you
can go to: http://www.vaisala.com. The model number
is GMW21D. This is designed for shelf or wall mount and is the only model in this series
that has a digital readout. These models also have a built in transmitter for high end
users who have recorders in their laboratories. The cost of the monitor at the retail
outlet is $505.00. Cole Parmer is one mail order company where this item can be purchased.
There are four choices of ranges that the monitor can be calibrated for at the factory.
These are 0 - 2000 ppm, 0 - 5000 ppm, 0 - 10,000 ppm and 0 - 20,000 ppm. The one that I
use is calibrated to 0 - 2000 ppm and is suited for our purpose. So if ordering one, tell
the order taker you want the 0 - 2000 calibrated one. The instrument is designed to
operate at 24 vac/vdc. It does not include a power supply. You can purchase one at any
electronics store for about $12.00. I am using a 24 volt ac adapter from Radio Shack, part
#11328010, 120 vac to 24 vac. There is a recommended interval of 5 years between factory
calibrations.
Here are two web sites to see more
information on Indoor and outdoor Air Pollution:
I would like to point out that Indoor Air
Quality is the homeowner’s responsibility and the Environmental Protection Agency can
only advise on maximum exposure levels by setting standards. It is up to the homeowner to
abide and take precautions on the many products we use around the home that will
contribute to the over-all pollution levels found in the home environment. I hope this
article stirred your interest. The EPA has performed studies in private homes and has
found levels of toxic chemicals that are five to 10 times higher then found in outdoor
concentrations. Now what solution can you think of that could possibly absorb pollutants -
the answer is, Air-Water-Interface. It is my belief that the subject of Indoor Air Quality
will be the next new topic where questions of water quality are concerned.
If anyone has questions on this article, I
can be contacted at rjordan8@compuserve.com
or on CompuServe’s Aquaria/Fish forum.
