However, I feel we're talking apples and oranges here (esp since we don't know
what Geoff's system setup is :). With heavily planted systems, you're dead
on. Heck, on my rainbowfish aquarium at home, I'm getting ready to add
*nitrate* to help push the system forward... How different is that from the
"textbook"? ;)
In a system that *doesn't* rely on plants or some other oxygenating mechanism,
finely ground CO2 is a big, big no-no, and the aquarist would want to diffuse
as much CO2 off from the system as possible (injecting more is even worse).
Especially in a system that houses high dissolved oxygen requiring animals
such as riffle dwelling darters.
The only O2 generating mechanism (besides surface gas exchange) in this system
is algae (which does a substantial amount of oxygenating). However, if there's
a canister filter on this type of less-natural system, the bacteria
respiration in the canister alone is going to counter that, in my opinion.
Which means when the algae are not releasing their products of photosynthesis
at night, the system is in grave danger of oxygen depression or depletion.
Add to this DO2 depression a supersaturation of CO2 and nitrogen (maximizing
the potential availability of those molecules), and you get animals
whirlygigging all over the place. Once the algae go to "bed" at "night", it
gets deadly, and right quick.
What's amazing is you can take them from this whirlygigged disposition, move
them to a more stable DO2 environment, and they bounce out of it like magic.
I "worked" with this indepth at my fish shop, with all sorts of lab grade
probes and what not. I can type up the scenario later on, if we think this
would be of some benefit to understanding how I observed animal health in
concern to DO2 and photosynthesis. Certainly not worthy of a real paper, but
the modest anecdote's results were quite impressive, and certainly changed the
way I view my aquaria.
Todd
-----Original Message-----
From: John Bongiovanni
Those of us (me anyway) with Native plants with our Native fish who use CO2
injection to "fertilize" the plants always have our effluent enter under the
water for those exact reasons. Surface aggitation will allow the CO2 to
escape and cause a pH rise in the water. My CO2 enters through the intake and
is dissolved as it goes through my canister filter. I use a diffuser bar
located near the bottom on the back of the tank to reduce the current effect
on the plants.
There has to be plenty of O2 in the tank due to the plants and CO2 has kept
the water at 6.8 - 7.0 pH. Without the CO2 the pH tends to range in the high
7's to low 8's.
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