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CO2 questions

>There are a lot of postings that try and explain the relationship of CO2,
>pH, and Kh.  All of them without exception are hard to follow.  I know I am
>a dumbie:-) but could someone please put it in very simple terms, please try
>not to write it like a thesis, but rather in very simple terms.
>I would like to know, without being to confused how I can look at the pH #,
>then turn to the Kh# and decide if the CO2 # is correct.  I really, really
>don't get it.  I'm sorry, but I must know.  

1. Go to the Krib web site, and find the KH/pH CO2 chart.  
2. Look up the KH of your tank water.
3. Look up the pH of your water
4. Where these line cross on the chart will be the concentration of CO2 in
your water.

(The above assumes that you have not used phosphate based buffers in your
tank, and are not using large quantities of peat)

It really doesn't get much simpler than that.  You can fiddle with KH by
adding carbonate buffers, or you can add CO2.  Either of these changes will
change the pH.  You can't "add" pH, because pH is a measurement, not a
"thing" you can add or subtract.  You can only affect the pH reading by
changing some other parameter. (by adding an acid or buffering substance)

>Krandall wrote how to know if
>the tank is saturated or not.  I would really like to understand this also.

You don't _want_ a tank "saturated" with CO2, believe me.  You won't have
any live fish long before you get there, and I doubt the plants could take
it for long either.  I'm not even sure what the saturation level is, but
it's way higher than we need.  You need _only_ enough CO2 to support the
growth of the plants in your tank without them resorting to meeting their
carbon needs by splitting carbonates/bicarbonates from the water column.
(which will lower the KH over time)

>As things stand, I have a 20 gl, that bubble one every second.  My pH is a
>constant 6.8 and my Kh is 2 or 3. 

Then if you KH is 2, you have about 9.4 mg/L of CO2, and if it is 3, you
have about 14 mg/L.  Both are within the acceptable range, though I tend to
run slightly higher than that. (I also use strong lighting and feed my
plants quite heavily)

> I wait until my fish go to the top
>sucking air before cutting back. 

If your KH is _really_ 2-3, and your pH is _really_ staying constant at
6.8, your fish should not be gasping from CO2.  OTOH, unless you are using
a pretty inefficient form of delivery, it seems like 1 bubble per second is
probably on the high side for a small tank like that.  I don't use a lot
more than that in my 125G tank, and with a KH of 5, my pH is 6.8 giving me
a CO2 concentration of about 23 mg/L.  My fish are not the least bit
stressed.  I have a feeling one of your test kits may be feeding you
inaccurate information.

> I know this is the wrong way of doing it,
>but I am learning from the experts on the list.  My hats off to you folks,
>you really have it nailed down, but tend to forget that some of use never
>had college chemistry.  If some one could put things in "layman's" terms
>that would gratefully appreciated.

I never even took high school chemistry.  It can take some time to learn
this stuff, but it's well worth the effort.