Re: [Killietalk] Nitrogen, nitrate, nitrite and ammonia

[Tyrone Genade <tgenade at gmail_com>]

Hello Lorraine

On Thu, 25 Nov 2004 10:38:15 -0700, Lorraine <overall077 at lycos_com> wrote:

> I assume that the plants
> were taking in O2 and putting out CO2, effectively starving the fish of O2.
> So I think with adequate light for the plants to take up CO2 and release O2
> all is well, but without the light you will have trouble.

I'm told (by my Botany prof) that all water plants are practice CO2
fixation at night. These are terms CAM plants (Crassulacean Acid
Metabolism). These plants will fix CO2 at night in the form of malic
acid. They will release NO CO2 under any circumstances. Because CO2
isn't as available under water as above it aquatic plants don't want
to let any get away.The pH decline you see is because the plants are
using the CO2 as much as the do at night and there are many bacteria
and fish that are producing it.

The major problem is that with the lights off the plants are no longer
using the CO2 and making O2 but are instead using O2. As planted tanks
tend to be very dense with plants they end up consuming large amounts
at night. Without proper aeration the tank O2 levels drop
considerably.

Without a high enough O2 level the CO2 in the wate (that isn't
normally toxic) can force the O2 off the hemoglobin and suffocate the
fish. It is the same situation with NO2-.

The heme has an affinity to O2, CO2, NO2- and CO. This affinity is
fixed by its chemistry but the actual binding is concentration
dependant. The O2 concentration has to decrease relative to the
inhibitor (e.g. CO2) before it becomes a problem.
 
Hemoglobin has a higher affinity for CO and CO2 than it does for O2
but the blood chemistry is such that CO2 is mostly in the form of
HCO3- which has a lower affinity for O2 and so the fish is able to
deal with a little CO2. As the CO2 in the water increases and the O2
declines the blood pH drops and more HCO3- become CO2. Without the O2
present at high concentrations the CO2 simply forces it off the
hemoglobin and the fish suffocates.

Regards
-- 
Tyrone Genade
http://tgenade.freeshell.org
email: tgenade at freeshell_org; MSM: tgenade at hotmail_com
tel: +39-334-379-5654 (cell)
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