The thing in calcium carbonate that does the buffering is the
carbonate, not the calcium. Don't know anything about plaster of
paris, but calcium sulfate is different from calcium carbonate.

Carbonate exists in water as an equilibrium between carbonate ion
(CO2, with a charge of -2) and bicarbonate ion (HCO2, with a charge of
-1). It has the ability to pick up or drop a hydrogen ion (H+). It's
the amount of free hydrogen ion that determines pH,

I'm not a chemist, but maybe the sulfate doesn't have the same
buffering capacity as carbonate.

Joan
___________________


Calcium carbonate, in the
form of calcium sulfate, increases the KH when introduced into the
water at a pH of 7.8 . So how does increased levels of calcium
carbonate cause wild pH swings?

Regards,

Hal

On Sat, 12 May 2007 14:53:35 CST, wrote:

dont know, but when those "pills" are tossed into soft acid ponds the
pH swings are enough to start killing the fish. It sounds good in
theory, just doesnt work. Another Koivorkian moment.
Ingrid

I suspect this was something you heard about instead of personal
experience and the pH pill you heard about was more than just Plaster
of Paris, or one with additives to enhance molding qualities, like
silica. I don't know what else might be used, possibly quick lime or
one of those used in cement for quick setting?

I've had more success at raising the KH along with the GH, instead of
just raising the GH with limestone's by using calcium sulfate, in the
pH pill than any other substance. I must admit it is difficult to
find a plaster of Paris without additives. I haven't tried one with
quick lime though .

Regards,

Hal

On Sat, 12 May 2007 17:19:26 CST, Joan wrote:

I'm not a chemist, but maybe the sulfate doesn't have the same
buffering capacity as carbonate.

Let me try again. The calcium sulfate (plaster of Paris.) when
dissolving into the water carries calcium carbonate into solution.
Calcium carbonate in limestone stops entering solution when the pH of
the water reaches 7.8. Sorry if I mislead you, but I thought Ingrid
knew that. You are correct in wanting calcium carbonate to buffer KH,
so do I. However calcium can also enter the water and register on a
tester as GH, but I want calcium carbonate in the water and to
register as KH on my test kit.

I'm not a chemist either, just a dummy with soft water and a few
experiences, trying to learn something.

Regards,

Hal

wrote:

dont know, but when those "pills" are tossed into soft acid ponds the
pH swings are enough to start killing the fish. It sounds good in
theory, just doesnt work. Another Koivorkian moment.

You're a scientist, Solo; you should know better. Plaster of Paris does not
cause wild pH swings. It sounds good in theory, _and_ it works. It
doesn't work in the _long_ term because the buffer gets used up, but it
does work.
--
derek
- Unless otherwise noted, I speak for myself, not rec.ponds.moderated
moderators.

It does in some water. I am not a chemist either, and I am simply too
old and busy with other stuff to dig out my chem books and start
re-learning what I would need to know to work thru this.

at least in soft acid water using calcium sulfate causes up and down
PH swings. carbonate wont for the reasons you gave. perhaps sulfate
has a much greater dissociation potential (I am grasping at parts of
my memory have not been accessed for nearly 30 years!)

It is like people used to recommend vinegar to acidify the water. Good
idea, but it is organic and soon the water contains enough bacteria
that uses acetic acid as a food.

Ingrid

On Sun, 13 May 2007 15:06:57 CST, Derek Broughton
wrote:

wrote:

dont know, but when those "pills" are tossed into soft acid ponds the
pH swings are enough to start killing the fish. It sounds good in
theory, just doesnt work. Another Koivorkian moment.

You're a scientist, Solo; you should know better. Plaster of Paris does not
cause wild pH swings. It sounds good in theory, _and_ it works. It
doesn't work in the _long_ term because the buffer gets used up, but it
does work.

The Goldfish Guru lives in Alabama. People started calling her after
their Koi started dying (she had training in fish diagnosis mostly for
the catfish farms down in Ala). She was checking their pH and finding
this wild swinging that isnt normal for Ala. That is when she found
out they were dropping these plaster of paris "pills" into their
ponds. when they removed them, the swinging stopped. this was a few
years ago, dont know if people still do it.
I live where they "mine" the limestone for export. So I have ponds
out at the dacha that are filled with well water. At the same time,
we have a water softener and filled my tanks with water with no buffer
at all and had to add it back. Now I live in the city with water out
of the lake, soft water and have to add hardness. WHAT to put into
the tank and what NOT to put in the tank is of great concern. I used
to use organic dolomitic limestone (walmart) and then the quit selling
it. Now I use the liquid stuff I mentioned before. I just want
people to be careful. Ingrid

On Sun, 13 May 2007 10:19:51 CST, Hal wrote:
I suspect this was something you heard about instead of personal
experience and the pH pill you heard about was more than just Plaster
of Paris, or one with additives to enhance molding qualities, like
silica. I don't know what else might be used, possibly quick lime or
one of those used in cement for quick setting?

I've had more success at raising the KH along with the GH, instead of
just raising the GH with limestone's by using calcium sulfate, in the
pH pill than any other substance. I must admit it is difficult to
find a plaster of Paris without additives. I haven't tried one with
quick lime though .

Regards,

Hal

calcium sulfate puts calcium and sulfate into water.
calcium carbonate puts calcium and carbonate into water.
bicarbonate is the buffer system of living things.
the dissociation constants are different, maybe one is affected by pH
or by temp more than the other. Like I said, too old for this.
Ingrid

On Sun, 13 May 2007 10:20:16 CST, Hal wrote:

On Sat, 12 May 2007 17:19:26 CST, Joan wrote:

I'm not a chemist, but maybe the sulfate doesn't have the same
buffering capacity as carbonate.

Let me try again. The calcium sulfate (plaster of Paris.) when
dissolving into the water carries calcium carbonate into solution.
Calcium carbonate in limestone stops entering solution when the pH of
the water reaches 7.8. Sorry if I mislead you, but I thought Ingrid
knew that. You are correct in wanting calcium carbonate to buffer KH,
so do I. However calcium can also enter the water and register on a
tester as GH, but I want calcium carbonate in the water and to
register as KH on my test kit.

I'm not a chemist either, just a dummy with soft water and a few
experiences, trying to learn something.

Regards,

Hal

OK, I went back and did a search. This message was from Rod Farlee
who IS a chemist. this is what he said on 6/16/1999
Ingrid

"But this "pH pill" is not the "one size fits all", "toss it in and
forget it" remedy that the ******** suggests it is.

It certainly works, but with some caveats. It raises GH (general
hardness, calcium) more than calcium carbonate (limestone) alone
does. That's because it contains calcium sulfate (gypsum), which
is much more soluble than calcium carbonate, and which raises
GH but not KH (alkalinity, bicarbonate).

So unless one has very soft, slightly alkaline water to begin with,
care should be taken. GH and KH should both be monitored.
If GH is getting too high, take it out, and add baking soda if needed
to raise KH. Or limit the amount to less than 1 lb/1000 gallons, to
ensure GH does not continue to rise.

If much larger amounts of plaster of Paris are added, it just won't
work. Gypsum is 170 times more soluble than calcite. Gypsum
will continue to dissolve, and push GH "off the scale". Through the
common ion effect (calcium), this will suppress dissolution of the
calcite (calcium carbonate), so KH will remain low. If a very large
amount were used, GH and pH would go up, and KH would actually
go down, and the pond might get cloudy with calcite precipitation.
That would be a Bad Thing: it's the next step on the road to an
alkali lake. Gotta watch for that.

Happily, it takes some weeks for the "pH pill" to dissolve anyway,
so these gradual changes can be monitored. And the effects of an
"overdose" are ameliorated if one's water contains a substantial
magnesium component in it's GH (the average eastern or
midwestern river does, Ca/Mg ~ 4). (Reasons: MgCO3 is much
more soluble than CaCO3, and it interferes with calcite cystallization
so allows supersaturation to occur. This reduces high GH driving
KH down.) Finally, if one receives regular rainfall, one might never
see these overdose effects. But the potential is there, and I treaded
close to it before I understood what was happening."

I know nothing about calcium and ponds, however calcium carbonate rock
(and to a very much lesser extent, calcium sulfate) is something I
have been involved with for many years. Calcium sulfate, or gypsum,
forms some caves, but is most commonly encountered as speleothems
(formations) in limestone, or calcium carbonate,, largely as gypsum
"flowers" or needles. Early on in cave exploration, most cavers used
lamps powered by calcium carbide and water. When calcium carbide
reacts with water, it gives off acetylene, which is burnt, the "spent"
carbide consisting mostly of calcium hydroxide. Caves are formed
largely when carbon dioxide is dissolved in surface water which forms
a weak acid solution which in turn dissolves the limestone, slowly
resulting in a cave. To be sure, there are other contributors to
speleogenesis, but this is a very common cause. I not a chemist, and
not a limestone hydrologist either, but I can't help but feel that
calcium hydroxide and dissolved carbon dioxide play a role in this
also.
--
Galen Hekhuis
I may have mispoken

wrote:

OK, I went back and did a search. This message was from Rod Farlee
who IS a chemist. this is what he said on 6/16/1999
Ingrid

"But this "pH pill" is not the "one size fits all", "toss it in and
forget it" remedy that the ******** suggests it is.

Thanks Ingrid - I can live with that :-)
--
derek
- Unless otherwise noted, I speak for myself, not rec.ponds.moderated
moderators.

On Mon, 14 May 2007 08:35:20 CST, wrote:

OK, I went back and did a search. This message was from Rod Farlee
who IS a chemist. this is what he said on 6/16/1999
Ingrid

"But this "pH pill" is not the "one size fits all", "toss it in and
forget it" remedy that the ******** suggests it is.

It certainly works, but with some caveats. It raises GH (general
hardness, calcium) more than calcium carbonate (limestone) alone
does. That's because it contains calcium sulfate (gypsum), which
is much more soluble than calcium carbonate, and which raises
GH but not KH (alkalinity, bicarbonate).

So unless one has very soft, slightly alkaline water to begin with,
care should be taken. GH and KH should both be monitored.
If GH is getting too high, take it out, and add baking soda if needed
to raise KH. Or limit the amount to less than 1 lb/1000 gallons, to
ensure GH does not continue to rise.

Thank you Ingrid!
I'm sorry if you had to work a bit harder than you wanted to, but I
appreciate the information.

It is more a mystery now, more than ever as to why I got higher KH
readings after putting plaster of Paris into my pond, if it only
raised the GH, however I shall consider this a lesson learned.
(Not universal)

Regards,

Hal