Coral, CO2 controller, KH, and [CO2]

[[email protected]]

Hi folks,

Here's a 'speriment I'd like to try. Since it's so obvious, though, I
bet it has occurred to some of you to try. So I'll describe it, and
wait for you to tell me the answer, for I am lazy. haha.

My hypothesis is that where a hunk o' coral is placed in a tank with
CO2 injection and a pH controller, and where the pH is set to somewhere
in the low sixes, the following will happen:
1.) pH will be maintained at that value to which the monitor is set.
2.) KH will go up, up, up as coral dissolves
3.) GH will go up, up, up as coral dissolves
4.) As a result of constant pH and rising KH, [CO2] will go up, up,
up.

There will, of course, be some sort of endpoint. I'm not sure what it
is. The core practical question is whether the above setup will end up
dissolving lethal (to fish) amounts of CO2 in the water. I suspect it
can.

WITHOUT CO2 injection, I suspect what would happen is just a longterm
increase in GH and KH, but CO2 will stay constant at atmospheric
equilibrium.

Thoughts?

--Trapper

[NetMax]

> wrote in message
oups.com...
> Hi folks,
>
> Here's a 'speriment I'd like to try. Since it's so obvious, though, I
> bet it has occurred to some of you to try. So I'll describe it, and
> wait for you to tell me the answer, for I am lazy. haha.

I won't try it either, and I also don't know what will happen, but it's
not too much work to just type, so here goes my ideas.

> My hypothesis is that where a hunk o' coral is placed in a tank with
> CO2 injection and a pH controller, and where the pH is set to somewhere
> in the low sixes, the following will happen:
> 1.) pH will be maintained at that value to which the monitor is set.

Assuming infinite supply (CO2 tank and not DIY) then yes.

> 2.) KH will go up, up, up as coral dissolves

Actually the rate of dissolution (is that a word?) will increase as the
water becomes more acidic.

> 3.) GH will go up, up, up as coral dissolves

Ditto here, yes.

> 4.) As a result of constant pH and rising KH, [CO2] will go up, up,
> up.

Here is where you have the potential for discrepancy. I think it will
take a lot more CO2 to maintain a high CO2 saturation level, because at
higher kH/pH, the CO2 will want to equalize to a much lower level faster
(see comment on infinite CO2 above).

> There will, of course, be some sort of endpoint. I'm not sure what it
> is. The core practical question is whether the above setup will end up
> dissolving lethal (to fish) amounts of CO2 in the water. I suspect it
> can.

I think the endpoint will be a function of the coral's surface area and
rate of decay as a ratio of the total water, so with a CO2 tank, you
might visibly see your coral shrinking (or at least it will break up and
leave you with a lot of ground particles slowly turning to smaller bits).
Eventually, chemically, that endpoint should move to tax your system's
ability to maintain that level of acidity. It will probably be a
significant amount of carbonic acid.

> WITHOUT CO2 injection, I suspect what would happen is just a longterm
> increase in GH and KH, but CO2 will stay constant at atmospheric
> equilibrium.

Nope, I think the CO2 level would decrease.

> Thoughts?
>
> --Trapper

Like I said, just semi-educated guesses from me.
--
www.NetMax.tk

[steve]

Okay, I'll be a guinea pig, sort of... I'm injecting C02 from a tank.
I don't use a controller though, so input is constant. My water out of
the tap is very soft at 3dGH and 2dKH. To avoid a pH crash while
injecting C02, it was advised I raise my KH to a minimum of 3dKH.
Rather than adding baking soda to every water change, I chose to use
crushed coral bits. I dropped 1/2 cup into the tank and monitored the
pH and KH. With the bubble rate constant, the pH dropped from 6.8 to
6.6, and the KH went up from 2d to 3dKH. I tossed in another handful
of coral and the KH has now topped out at 3.5dKH.

I think my only concern is I may use up the coral and could suffer a pH
crash when it's gone. So, I piled it all up in one spot and I can keep
an eye on that.

steve

[[email protected]]

NetMax wrote:
> > wrote in message
> oups.com...
> > Hi folks,
> >
> > Here's a 'speriment I'd like to try. Since it's so obvious,
though, I
> > bet it has occurred to some of you to try. So I'll describe it,
and
> > wait for you to tell me the answer, for I am lazy. haha.
>
> I won't try it either, and I also don't know what will happen, but
it's
> not too much work to just type, so here goes my ideas.
>
> > My hypothesis is that where a hunk o' coral is placed in a tank
with
> > CO2 injection and a pH controller, and where the pH is set to
somewhere
> > in the low sixes, the following will happen:
> > 1.) pH will be maintained at that value to which the monitor is
set.
>
> Assuming infinite supply (CO2 tank and not DIY) then yes.

Yep. I guess "CO2 injection" can mean DIY to some people, so I should
have been more precise. I assume here a goodly-sized CO2 tank. I
canna' give you moor than tha', cap'n.


> > 2.) KH will go up, up, up as coral dissolves
>
> Actually the rate of dissolution (is that a word?) will increase as
the
> water becomes more acidic.

Aha, but the water here will not become more acidic! It will track a
set pH, as per the pH controller setpoint. And it will not become more
alkaline, either, since the co2 tank is large and can counter any such
influence.

>
> > 3.) GH will go up, up, up as coral dissolves
>
> Ditto here, yes.

As an aside, you don't happen to know a typical Ca/Mg ratio in coral,
do you?

> > 4.) As a result of constant pH and rising KH, [CO2] will go up,
up,
> > up.
>
> Here is where you have the potential for discrepancy. I think it
will
> take a lot more CO2 to maintain a high CO2 saturation level, because
at
> higher kH/pH, the CO2 will want to equalize to a much lower level
faster
> (see comment on infinite CO2 above).

Put simply, what you're saying seems to be that the greater the
difference in actual dissolved CO2 and equilibrium CO2 (commonly said
to be 2-3ppm) then the more dissolved CO2 "wants" to escape to the
atmosphere. To wit: a glass of seltzer at 1 atmosphere pressure will
outgas, with respect to CO2, until the CO2 is equilibrated (at the same
time it may well be in-gassing with respect to other gases! Ha!)

> > There will, of course, be some sort of endpoint. I'm not sure what
it
> > is. The core practical question is whether the above setup will
end up
> > dissolving lethal (to fish) amounts of CO2 in the water. I suspect
it
> > can.
>
> I think the endpoint will be a function of the coral's surface area
and
> rate of decay as a ratio of the total water, so with a CO2 tank, you
> might visibly see your coral shrinking (or at least it will break up
and
> leave you with a lot of ground particles slowly turning to smaller
bits).
> Eventually, chemically, that endpoint should move to tax your
system's
> ability to maintain that level of acidity. It will probably be a
> significant amount of carbonic acid.

My CO2 reactor can dissolve a *lot* of CO2. So it sounds like there'd
be dead fishies. Needless to say, there will be no piscine test pilots
in my experiment.

>
> > WITHOUT CO2 injection, I suspect what would happen is just a
longterm
> > increase in GH and KH, but CO2 will stay constant at atmospheric
> > equilibrium.
>
> Nope, I think the CO2 level would decrease.

Are you saying that given a high enough KH it is possible to keep less
CO2 in the water than would be supplied by equilibration with the
atmosphere? To me it only seems possible if the KH can change the
equilibration point w.r.t. CO2, because there's always going to be the
constant such-and-such partial pressure of CO2 in the air. Hrm. I
shall have to think more about this in order to see if that is
possible. It may well be, but the answer will have to wait for my chem
textbook. :)


> > Thoughts?
> >
> > --Trapper
>
> Like I said, just semi-educated guesses from me.
> --
> www.NetMax.tk

I'm going away for a couple days soon. I've a mind to take my CO2
contraption out of my plant tank, and run this 'spearmint in a 5-gal
bucket. I suspect a couple days' worth of running will be enough at
least to show the beginning of the trend.

--Trapper

[NetMax]

> wrote in message
oups.com...
>
> NetMax wrote:
>> > wrote in message
>> oups.com...
>> > Hi folks,
>> >
>> > Here's a 'speriment I'd like to try. Since it's so obvious,
> though, I
>> > bet it has occurred to some of you to try. So I'll describe it,
> and
>> > wait for you to tell me the answer, for I am lazy. haha.
>>
>> I won't try it either, and I also don't know what will happen, but
> it's
>> not too much work to just type, so here goes my ideas.
>>
>> > My hypothesis is that where a hunk o' coral is placed in a tank
> with
>> > CO2 injection and a pH controller, and where the pH is set to
> somewhere
>> > in the low sixes, the following will happen:
>> > 1.) pH will be maintained at that value to which the monitor is
> set.
>>
>> Assuming infinite supply (CO2 tank and not DIY) then yes.
>
> Yep. I guess "CO2 injection" can mean DIY to some people, so I should
> have been more precise. I assume here a goodly-sized CO2 tank. I
> canna' give you moor than tha', cap'n.
>
>
>> > 2.) KH will go up, up, up as coral dissolves
>>
>> Actually the rate of dissolution (is that a word?) will increase as
> the
>> water becomes more acidic.
>
> Aha, but the water here will not become more acidic! It will track a
> set pH, as per the pH controller setpoint. And it will not become more
> alkaline, either, since the co2 tank is large and can counter any such
> influence.
>
>>
>> > 3.) GH will go up, up, up as coral dissolves
>>
>> Ditto here, yes.
>
> As an aside, you don't happen to know a typical Ca/Mg ratio in coral,
> do you?
>
>> > 4.) As a result of constant pH and rising KH, [CO2] will go up,
> up,
>> > up.
>>
>> Here is where you have the potential for discrepancy. I think it
> will
>> take a lot more CO2 to maintain a high CO2 saturation level, because
> at
>> higher kH/pH, the CO2 will want to equalize to a much lower level
> faster
>> (see comment on infinite CO2 above).
>
> Put simply, what you're saying seems to be that the greater the
> difference in actual dissolved CO2 and equilibrium CO2 (commonly said
> to be 2-3ppm) then the more dissolved CO2 "wants" to escape to the
> atmosphere. To wit: a glass of seltzer at 1 atmosphere pressure will
> outgas, with respect to CO2, until the CO2 is equilibrated (at the same
> time it may well be in-gassing with respect to other gases! Ha!)
>
>> > There will, of course, be some sort of endpoint. I'm not sure what
> it
>> > is. The core practical question is whether the above setup will
> end up
>> > dissolving lethal (to fish) amounts of CO2 in the water. I suspect
> it
>> > can.
>>
>> I think the endpoint will be a function of the coral's surface area
> and
>> rate of decay as a ratio of the total water, so with a CO2 tank, you
>> might visibly see your coral shrinking (or at least it will break up
> and
>> leave you with a lot of ground particles slowly turning to smaller
> bits).
>> Eventually, chemically, that endpoint should move to tax your
> system's
>> ability to maintain that level of acidity. It will probably be a
>> significant amount of carbonic acid.
>
> My CO2 reactor can dissolve a *lot* of CO2. So it sounds like there'd
> be dead fishies. Needless to say, there will be no piscine test pilots
> in my experiment.
>
>>
>> > WITHOUT CO2 injection, I suspect what would happen is just a
> longterm
>> > increase in GH and KH, but CO2 will stay constant at atmospheric
>> > equilibrium.
>>
>> Nope, I think the CO2 level would decrease.
>
> Are you saying that given a high enough KH it is possible to keep less
> CO2 in the water than would be supplied by equilibration with the
> atmosphere? To me it only seems possible if the KH can change the
> equilibration point w.r.t. CO2, because there's always going to be the
> constant such-and-such partial pressure of CO2 in the air. Hrm. I
> shall have to think more about this in order to see if that is
> possible. It may well be, but the answer will have to wait for my chem
> textbook. :)
>
>
>> > Thoughts?
>> >
>> > --Trapper
>>
>> Like I said, just semi-educated guesses from me.
>> --
>> www.NetMax.tk
>
> I'm going away for a couple days soon. I've a mind to take my CO2
> contraption out of my plant tank, and run this 'spearmint in a 5-gal
> bucket. I suspect a couple days' worth of running will be enough at
> least to show the beginning of the trend.
>
> --Trapper


re: Ca/Mg mix of calcium: good question.
re: non-injected CO2 equilibrium to atmosphere: it is not 1:1 and the
ratio is affected by the pH and kH values.
--
www.NetMax.tk