Re: Water chemistry
To: Aquatic-Plants at actwin_com
Subject: Re: Water chemistry
From: psears at NRCan_gc.ca (Paul Sears)
Date: Tue, 9 Jul 1996 09:01:21 -0400 (EDT)
In-Reply-To: <199607090739.DAA30758 at looney_actwin.com> from "Aquatic-Plants-Owner at ActWin_com" at Jul 9, 96 03:39:02 am
> > From: John Lobingier <jlob at wpa_net>
> (and from George)
(much snipping here and there)
> No, I do not use peat in this tank. I use no pH up or pH down chemicals.
> I do have two units ( bags ) of Dick Boyd's Chemi Pure in my Eheim
> canister filter. This a combination of carbon and ion exchange resins.
> It is marketed for saltwater fish, discus, and African Cichlids. It is
> suppose to keep the pH up. It is not keeping the pH up.
I would get this stuff out of there! You don't say whether
the ion exchange resin is a cation or anion resin, or both, or what it was
charged with in the first place, but it is quite possible that it
has been grabbing calcium and magnesium from the water (hence the
fall in GH), and also very effectively removing trace elements like
iron, copper, manganese and zinc (hence the plant problems).
> The pH is now at 6.2, down from 6.4. Could the baking soda
> ( sodium bicarbonate ) be throwing my test kits off?
> I use Tetra GH and KH test kits. In my problem plant tank ( 55 gal. )
> they now give me a GH reading of .5dh, and a KH reading of 2dh. They used
> to give me a GH reading of 7dh and a KH of .5dh. I also have an Aquarium
> Pharmaceuticals "general hardness" test kit. It says I have no hardness
> at all. I went out and bought a test kit by Wardley. It like the
> Aquarium Pharmaceuticals test kit says I have no hardness.
I'm not surprised if you have been putting ion exchange resins
in the filter. They will eventually run out of capacity, but it would
be easier to remove them.
> > > Is KH part of the GH?
The big problem with these terms is finding proper
(and consistent) _definitions_ for them!
> > In generally accepted *hobbyist* terms, KH is the measure of HCO3- and
> > CO3--; GH is the measure of Ca++ and Mg++. KH and GH are totally
> > separate.
Yes, and we are usually interested more in the bicarbonate
concentration (carbonate will be small), because of the carbonic acid
/bicarbonate buffering equilibrium.
> > However, typical hobbyist test kits seem to measure total *alkalinity*
> > or acid buffering and call the results "KH". If carbonates are the
> > only buffer in your water, i.e., the only contributor to alkalinity,
> > this is OK. If you have other buffers such as phosphates (from pH-UP
> > or -DOWN or other additives), the "KH" measurement is up for grabs.
Yes. The kits do a titration of the anions of weak acids
against a strong acid, ending at a fairly low pH. The indicator is
usually methly orange. You then get a measure of the amount of acid
required to change all the weak anions to their acid forms.
> > Some test kits measure "total hardness" which is a combination of
> > KH and GH. This type of measurement is of little value to us.
I think that these kits are in fact measuring GH (Ca++ and Mg++),
and _calling_ it "total hardness", which adds to the confusion! It
would be very difficult indeed to come up with a test that measured
Ca++, Mg++ _and_ "alkalinity" all in one test. If your test is one that
uses EDTA and has a red/blue endpoint, you are measuring Ca++ and Mg++.
> Tetra KH and GH kits are the ones I use. The water company report says
> our water has an alkalinity level of 10mg/l.
Hmmmmmm. 10 mg of _what_ per litre? I suspect that they are
referring to mg of "calcium carbonate" per litre, meaning that the
"alkalinity", or acid neutralizing capability of 1 litre of the water
is the same as that provided by that much calcium carbonate. It
is consistent with your KH measurements, if that is the case.
> > Just so I don't get flamed yet again by our chemistry professionals,
> > "KH" and "degrees" are scientifically undesireable terms. But since
> > the test kit makers continue to use them, so will I.
The problem is that we have borrowed old terms from people
who were interested in municipal water treatment and boilers, and have
then applied them in rather different situations. This would not
have mattered if the definitions had been nailed down first.
There is no problem using any unit you like, provided the
definition is clear, unambiguous and easy to find!
> > > Calcium carbonate will raise the GH, but not the KH?
> > The calcium ions will raise GH and the carbonate ions will raise KH.
Yes, but don't forget that KH is actually bicarbonate, formed
CO3-- + H2O + CO2 <-> 2HCO3-
> > George
> Any ideas on all of this? I am ready to scrap my 120 watts of light, and
> the CO2, and give my lonley sword plant its 40 watts of light back. :)
Throw out the ion exchanger!!!!
Paul Sears Where did I put my flame thrower????