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Re: pH, KH confusion

> From: "Berryman, David" <DBerryma at AspenMed_org>
> Subject: CO2, Kh?, pH? I'm confused! Plus DIY light canopy, it's easy.
> 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.

	The CO2 concentration in the tank is set by the CO2 system, fish,
filters, etc., but is _not_ affected by anything dissolved in the water.

	The KH is set by the stuff dissolved in the water. (Not the CO2!)

	The CO2 concentration and the KH set the pH.

	The last statement assumes that bicarbonate/CO2 is the main
buffering system in the tank.  If there is a lot of phosphate, or any
other buffering system there, that may set the pH instead.

> 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.

	The ususal tables will tell you what the CO2 concentration is,
if you know the KH and pH.

>  I really, really
> don't get it.  I'm sorry, but I must know.  Krandall wrote how to know if
> the tank is saturated or not.

	I don't think she did.  Forget about saturation.  It isn't relevant.

> 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.

	Using the chart in the Krib, this implies a CO2 concnetration
of about 12 ppm (pH 6.8 and KH 2.5).  That should be fine.

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

	If the pH and KH numbers are good, and you don't have other buffering
systems in there, I think the fish are going to the surface for some other

>  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 think that high school math is all that's needed, once you
have the idea of an equilibrium constant for a reaction.  It's worth
going back to the "thesis" stuff and going through it step by step,
because it really is the simplest way of explaining it.  Please feel free
to e-mail me directly.

Paul Sears        Ottawa, Canada