Re: Re: ph Control

[cfonda@sentientconsult.com]

>The biggest problem I can see with CO2 to control pH for Apistos is that
the
>amount needed to get low pH values can be toxic to fish.  Standard charts
>relating pH, kH, and CO2 will show that you need low kH and fairly high
CO2 to
>keep the pH in the low sixes.  You  would probably need an electronic
>injection system and pH meter in order to avoid wild pH swings and toxic
CO2
>levels.
CO2 levels have to get above around 20 ppm before they become even mildly
toxic to fish.  The great thing is that the CO2 will not displace the O2
from the water.  As long as your filters provide at least mild to moderate
surface agitation, CO2 levels should not become toxic.  You will, however,
see a pH flux in phase with the day-night cycle of the plants unless you
are willing to go the expense of getting a digital pH controller and
solenoid valve (about $150 to $300 worth of extra equipment beyond the
basic CO2 injection system).  This pH shift should not be harmful to your
fish or plants. (Make sure you are using plants that like acidic water...
the plants will benefit greatly from the CO2.)

The CO2 system will build up the buffering in your tank, actually, through
production of carbonic acid -- H2CO3 -- this is the primary buffer in most
biologic systems, including the human body.  Carbonic acid will not
increase carbonate hardness because carbonate hardness is more a measure of
calcium ions in the water, most easily measure by measuring the amount of
calcium carbonate (Ca(CO3)2).  Increasing the carbonate CO3 (2+) does not
increase the amount of Ca (2-), so buffering is achieved without increasing
hardness.

>That's where having an extra organic buffer like peat would help.

Running peat in your filter will definitely help things... just remember to
change the peat about once every 2 weeks.

>I posted a question regarding peat buffers and CO2 injection a couple of
months ago but
>no one answered it.  I wondered how to calculate CO2 concentration in such
a
>system since the charts are calculated with carbonate buffers only.
Perhaps
>one of the chemists could help us here.

The charts are calculated with carbonate buffers because a
H2CO3 -- HCO3 (-) + H+ -- CO3 (2-) + 2H+
chemical system is what is actually responsible for the pH shift and
buffering provided by CO2 injection.  KH provides the same buffering via
Ca(CO3)2 as opposed to CO2, so your charts should be accurate.  Just
remember that KH is a measure of ions that bond to carbonate... the
carbonate itself does not make the water hard.

- --Cliff