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  1. Oxygen test & 02 staturation question
    by booth-at-hplvec.LVLD.HP.COM (George Booth) (13 Jan 92)
  2. aeration and circulation concerns
    by (George Booth) (17 Feb 1995)
  3. O2 levels
    by "James Purchase" <jpurch/> (Thu, 24 Aug 2000)
  4. oxygen versus co2
    by "Roger S. Miller" <rgrmill/> (Tue, 20 Mar 2001)

Oxygen test & 02 staturation question

by booth-at-hplvec.LVLD.HP.COM (George Booth)
Date: 13 Jan 92
Newsgroup: alt.aquaria

In alt.aquaria, (Richard Clark) writes:

    The saturation level for O2 in freshwater at 80F is approx 8.1ppm

At sea level, of course.  At higher altitudes, it decreases.


aeration and circulation concerns

by (George Booth)
Date: 17 Feb 1995
Newsgroup: rec.aquaria

Matthew J Blackford ( wrote:
> So I guess the bottom line is:  is a localized violent disruption of the
> water surface a more effictive method of providing oxygen than a gentle
> circulation of the entire water surface?

Generally, good circulation is enough to provide good oxygenation. 
The best you can do is to reach 100% O2 saturation - to get more 
O2 requires a pressurized reactor or live plants.  Two hundred
airstones run by 200 Tetra Luft pumps won't get you any more. 

The only way to tell is to measure it, but dissolved O2 kits are the 
more expensive of the test kits (at least, for ones that actually work). 

If your fish aren't gasping for air at the surface, your O2 levels are
just fine. 

George Booth                         "Nothing in the world is more dangerous             than sincere ignorance and conscientious 
Freshwater Plant Tank Technology     stupidity" - Martin Luther King, Jr. 

O2 levels

by "James Purchase" <jpurch/>
Date: Thu, 24 Aug 2000

John wrote:

"I'd just like to know what range of acceptable tritation tube readings are
for this kit."

I could be snarkey and merely say that the O2 level of the water in your
aquarium should be at or very close to saturation levels at all times. After
many years of monitoring my planted tanks, the only time the O2 levels have
ever dipped has been when I got lax with maintenance and the BOD of the tank
exceeded the plants abilities to release O2 into the environment.

However, since you don't have lots of plants and want to have lots of fish,
I would still advise you to maintain the O2 levels at or very close to
saturation levels. Make sure that you don't let waste products build up in
the tank (bacterial decomposition of organic wastes will consume O2), keep
the water moving (good circulation will promote gas exchange at the
air/water interface).

For anything further, may I suggest the following URL:

There is a table there which will give you the saturation values for waters
of various salinities and temperatures (at sea level). It also has detailed
and very clear instruction on how to conduct Winkler Method DO measurements
(such as your LaMotte test kit).

Good luck,

James Purchase

oxygen versus co2

by "Roger S. Miller" <rgrmill/>
Date: Tue, 20 Mar 2001

Lazarus Miskowski wrote:

> Some prominent members of the list (the names escape
> me at the moment) have long been proponents of
> increased oxygen levels in our tanks.  Generally this
> means increased ciculation.

This isn't necessarily true.

> My recent experience has
> been that fish activity level was increased by
> increasing circulation.  So I am a believer in this
> regard.
> My question has to do with maintaining co2 levels.
> High co2 and high oxygen aren't mutually exclusive,
> correct?

Their concentrations aren't directly related to each other in any way.

Circulation or aeration will usually keep the oxygen level in an
unplanted tank from falling too low for it's usual occupants.  It won't
rise much over 8 mg/l, because water reaches equilibrium with
atmospheric oxygen somewhere near 8, depending on temperature, altitude
and the composition of your home's interior air.

Photosynthesis by healthy plants in a well-lit aquarium can push the
oxygen content over 10 (that's where my old oxygen kit pegged out). 
That's a higher concentration than you can ever get from circulation
alone.  Circulation and aeration tend to keep the oxygen content close
to atmospheric equilibrium levels -- keep it *lower* than the
concentrations you would get without circulation.

Oxygen levels drop when the lights go out, the more circulation you
provide, the faster they drop.  A tank is unlikely to maintain elevated
oxygen levels all night, with or without circulation.  Just how low they
drop depends on the conditions in your tank.  The tank I used to monitor
had about 8 mg/l of oxygen before the lights came on in the morning.

People sometimes report that their fish are gasping at the surface in
the morning, implying low oxygen.  I've never seen that happen in my
tanks and I have to suspect that those tanks with gasping fish contain
more fish than I normally maintain in an aquarium and/or the plants
aren't photosynthesizing enough to supersaturate the tank.

> I can increase circulation and therefore
> increase oxygen, and at the same time increase my
> input of co2 to maintain adequate levels, correct?

This might get you a net increase in oxygen if your tank is overloaded
with fish, if you don't have very many plants, or if your plants aren't
real healthy.  It won't do your plants much good, and since the plants
are net producers of oxygen your increased circulation could end up with
an overall decrease in oxygen.

> While this may be inefficent, co2-wise, I presume it
> is healthier for the fauna.  Any comments?  Am I
> headed in the right direction?

It is inefficient -- maybe to the point of being self-defeating -- and
certainly it's something you don't need to think about much unless your
fish show symptoms of low oxygen.  If they are stressed by low oxygen
then it would probably be better for all concerned to reduce the fish

Roger Miller

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