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Re: CO2


You are correct Steve. My statement might have caused some confusion. 
Understanding the relationship between KH, CO2 and PH is essential. 
The main thrust of my comment was geared at the fact that in my 
opinion, it is not a good idea to use CO2 as a means to artificially 
lower the PH of the water below it's normal equilibrium level. 
Effects could be a rapid rise in PH in the event of a power outage on 
a solenoid system or a rapid rise in the event of the CO2 
bottle/source becoming empty.

This topic is relevant to the fact that fish are usually somewhat 
adaptable. It is better to keep a fish slightly outside it's desired 
parameters than to keep one in which the parameters are constantly 
changing. (PH, Temperature etc...)

Steve: Thanks for clarifying my statement to everyone!

Menlo Park, CA

>Date: Fri, 15 Sep 2000 13:51:35 -0700
>From: "Dixon, Steven T. (BEn)" <stdixon at ben_bechtel.com>
>Subject: CO2
>Julius wrote:  "Someone mentioned that the CO2 dropped the PH to a level
>that made their fish happy. This is not a safe practice. If you have a power
>outage and your solenoid valve shuts off, the PH can rapidly jump putting
>stress on the fish. It's a bad idea to regulate PH with CO2.  If you need to
>lower your PH, use RO water and then use a buffer to maintain a certain
>This statement worried me and I thought it might mislead folks who don't
>understand the relationship among CO2, pH and KH.  CO2 does affect pH in all
>cases in a completely understandable and predictable way.  CO2 in
>conjunction with  KH does in fact "regulate" pH.  Full stop and in all
>cases. Nothing could be worse that using RO water and setting your KH to an
>arbitrarily low level (say below 2 degrees KH) and then ignoring the affect
>additional CO2 will have on pH.  CO2 will lower pH in every case based on
>the amount of carbonate hardness (KH) present in the water column.  If you
>supplement CO2 as many of us do, there is no getting around the fact that if
>the CO2 shuts off, the pH will rise.  How much is a function of KH and the
>rate at which the tank system reaches equilibrium with the air (2 - 3 mg/l)
>when the CO2 shuts off.  If you run the CO2 continuously (an many of us do)
>and don't use a solenoid or controller, the only time you CO2 will shut off
>is when the CO2 tank runs out of gas.  A two-gauge regulator will allow one
>to monitor this situation as closely as one wants.
>In my view there is simply no substitute for understanding the basic
>relationship among CO2, pH and KH.
>Regards, Steve Dixon in San Francisco

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