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Night time aeration
I've gone over the Amano literature that I have looking for references to
injecting Oxygen. If there are any, I can't find them, but I did find
reference to "night time aeration".
AJ Vo. 35 "pH and Your Planted Aquaria"
"It would be erronerous to say night time aeration should be refrained to
prevent the pH swing. It is true that pH increases when CO2 dissipates
during night time aeration. Primarily, the objective for addition of CO2 in
a planted tank is solely for the purpose of fertilization, it should not be
used for the regulation of pH. There is considerable evidence for night time
aeration to be carried out. It is a well known fact that photosynthesis of
plants occurs in the day and the stored energy is utilized during the night
for oxidation. Increased oxygen by means of aeration is essential to aid the
oxidation process. On top of the aquatic plant needs, the fish and
microorganism also require oxygen in the night for respiration."
Two things come to mind here - as I mentioned earlier, conducting a
Dissolved Oxygen test just before "lights out" and then comparing the
results with a second test done just before "lights on" the following
morning will give you an idea of how much Oxygen is being consumed by the
organisms and chemical processes within the tank over night. If the O2
levels in the morning are _seriously_ depleated (enough to cause the fish
distress), there might be a case for using an airstone to aerate the
aquarium during the night when the lights are out. But keeping the filter
clean (decomposition of organic matter uses oxygen) and removing uneaten
food and detritus on a regular basis should also be carried out to lessen
the demand for oxygen by things other than your fish. But I can find nothing
to indicate that he actually advocates the injection of pure O2 - regular
atmospheric air (with its 21% O2 content) ought to be more than enough.
Time and time again here on the APD, people say that they inject CO2 to
bring down their pH levels to some imagined "magic" level, usually at or
slightly below 7.0. They go thru hoops in order to avoid pH levels over 7.0,
often resorting to phosphate based buffers. The quote from Amano above,
while I can't vouch for the accuracy of the translation from Japanese, does
make it very clear the real reason we inject CO2 - it is for its value as a
fertilizer, not as a pH regulator. Now, THIS I can agree with 100%!