Re: Peat and pH
To: Aquatic-Plants at actwin_com
Subject: Re: Peat and pH
From: psears at emr_ca (Paul Sears)
Date: Fri, 24 Nov 1995 08:50:50 -0500 (EST)
In-Reply-To: <199511232039.PAA07264 at looney_actwin.com> from "Aquatic-Plants-Owner at actwin_com" at Nov 23, 95 03:39:02 pm
> From: Allen Sandifer <ibi007 at lion_connect.more.net>
> Date: Thu, 23 Nov 1995 11:16:23 -0600
> Subject: Peat & pH
> I am trying to lower the pH of my tap water naturally. As it comes from the
> tap the pH is 9.3, if I let it sit for about a month aerating it several
> hours a day it will drop to 8.1, which is rather confusing to me. Can anyone
> explain this to me?
How hard (carbonate hardness) is the water? If it is KH 3.8,
as implied below, this implies that it has a _very_ low CO2 content when
it comes from the tap, somewhere around 0.07 ppm. This will _increase_
when the water is exposed to the air, to about 0.5 ppm, from which I would
expect a pH of about 8.5. A CO2 content of about 1.1 ppm would give
you the pH you do get, 8.1.
> I want to make peat water and mix it with the tap water to lower the pH. I
> prefer not to use straight peat water because of the color, I would prefer
> water of a rather clear quality. In straight peat water what is the lowest
> pH that I can expect? Does the amount of peat have an effect on this.
> At present I have a Fluval 403 filtering water in a 30g trash can. The
> bottom 2 containers have a layer of filter floss in the bottom then filled
> with peat. The top container has the regular Fluval foam filter to help keep
> the small particles from getting in to the trash can. After about 2 hours of
> operation the pH dropped to 6.64 but this morning the pH was 6.98. The KH
> had went from 3.8 to 1. After the carbonate buffers are depleted will the pH
> start to drop again?
If you use peat filtering, you will be replacing the carbonate
buffering with organic acid buffering. The pH you get will depend on
how much of what acids and how much in the way of metal ions are in the
solution. Provided there are reasonable amounts of them in there, the
pH should be pretty stable, and since the peat filtering replaces HCO3-
with the organic acid anions, you should have enough.
You have gone from a solution with Ca++ and HCO3- with CO2 (H2CO3)
to one with Ca++ and (organic acid anion)- with (organic acid). This
will be brown. The peat filtering you did destroyed HCO3-, creating CO2,
which left the solution overnight. That is why the pH rose again.
> If I mix water with a pH of 8.0 with water that has a pH of 7.0 will I get
> water with a pH of 7.5?
The result will depend on the contents of the two solutions,
specifically what buffering agents are in them. If you used pure water
with a pH of 7.0 and a good buffer solution with pH 8.0, when you mixed
them you would get pH 8.0.
> Once I get the pH down to where I would like it to be which is around 6.8 if
> I add carbonate buffers back into the water will the pH go back up?
Yes, if you don't add CO2.
Paul Sears Ottawa, Canada.