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DIY CO2, pH not dropping

> Date: Thu, 19 Jun 1997 18:16:20 -0500 (CDT)
> From: Conrad Yang <cyang at ccwf_cc.utexas.edu>
> I have the DIY Yeast CO2 setup in a 10g tank with a small power filter
> (no airstones) ...  Anyway, I checked the pH and it was 7.2.  The pH
> of my other tank without CO2 injection is also 7.2.  In fact the tap
> water is 6.6!  What's going on here?

There are many things that determine pH, CO2 being only one of them. 

Let's see ...

What type of pH test kit do you have?  When you say "7.2" and "6.6",
how accurate do you think those numbers are?  Most hobbyist test kits
have a pretty poor resolution.  If you think the numbers are accurate,
then ...

Take some tap water and measure the pH.  Then put that smae water in a
jar and shake it vigorously.  Let it sit for awhile.  Recheck the pH.
If the pH is now higher, there was dissolved O2 in the water that
lowered its pH.  Check it again after a day.  

Do you know the KH or alkalinity of your water?  If you have higher KH
(say, 3 or 4 degrees), small amounts of CO2 may not change the pH that

> I must not be dissolving enough CO2 into the water.  I have lots of
> production from the bottle, and the plants look great, like I said.  

If you're happy with the plants, leave well enough alone. Trying to
add more CO2 may lower the pH too much and stress your fish.  You
should understand the CO2 chemistry better before you do anything