CO2, no need to measure KH ??

While I was looking at the usual chart relating KH - pH - CO2
I found that if I wanted a 'target' CO2 level of 15mg/l this always
resulted in a drop of pH of about 0.7 from the no-CO2 equilibrium
(atmospheric) level of 3mg (is that right ?) to the pH at the 15mg injected
level, for all KH values between 1 and 8
sorry for poor english, did that make sense ?

Doing the same for a target of 25mg the ph drop needed was 0.9 for all/any
KH water.

Similar, for a target level of 30mg/l required(resulted in) a drop of about
1.0 in the pH for all KH waters from KH=1 to KH=8 (ie. all the KH's that I
examined )

In other words, I dont need a KH test kit, all I need is a pH test
measuring the non-carbonated water and the carbonated(injected) water.

Am I losing my marbles, I've not seen any refs. on the internet to this,
they all require me to test the KH to know the mg CO2
What am I missing ?

Ooops, looks like I messed up my identity and spamtrap
sorry
,,, testing ,,,,

wrote:

While I was looking at the usual chart relating KH - pH - CO2
I found that if I wanted a 'target' CO2 level of 15mg/l this always
resulted in a drop of pH of about 0.7 from the no-CO2 equilibrium
(atmospheric) level of 3mg (is that right ?) to the pH at the 15mg injected
level, for all KH values between 1 and 8
sorry for poor english, did that make sense ?

Doing the same for a target of 25mg the ph drop needed was 0.9 for all/any
KH water.

Similar, for a target level of 30mg/l required(resulted in) a drop of about
1.0 in the pH for all KH waters from KH=1 to KH=8 (ie. all the KH's that I
examined )

In other words, I dont need a KH test kit, all I need is a pH test
measuring the non-carbonated water and the carbonated(injected) water.

Am I losing my marbles, I've not seen any refs. on the internet to this,
they all require me to test the KH to know the mg CO2
What am I missing ?

I only use a pH meter to determine the levels of CO2 in my aquariums at
any given moment. The KH is usually a constant, so you only need to ever
measure that once, unless you are producing your own KH level from a
reverse osmosis filter or rain water. Actually, it is sometimes possible
for KH to vary from your tap, especially if you live in a hot and dry
region. The water authorities will sometime switch water sources, one
with more rain water etc, thus changing the KH.

CO2 content is not the only substance that can reduce or affect your pH.
Phosphate is known for altering the pH. Acids leeching from decomposing
dead matter or even drift wood can affect it. So you may need to take
these issues into account.

Nikki

On Thu, 12 Jan 2006 15:36:11 +0000, Nikki Casali wrote:

wrote:

[20 quoted lines suppressed]

I only use a pH meter to determine the levels of CO2 in my aquariums at
any given moment. The KH is usually a constant, so you only need to ever
measure that once, unless you are producing your own KH level from a
reverse osmosis filter or rain water. Actually, it is sometimes possible
for KH to vary from your tap, especially if you live in a hot and dry
region. The water authorities will sometime switch water sources, one
with more rain water etc, thus changing the KH.

CO2 content is not the only substance that can reduce or affect your pH.
Phosphate is known for altering the pH. Acids leeching from decomposing
dead matter or even drift wood can affect it. So you may need to take
these issues into account.

Nikki

Yes, good points Nikki, thank you.

This all began with a post in another forum from a member who had a GH test
kit but no KH.
We were asked how to convert GH into KH for CO2 measurements !

While the discussion progressed I was looking at the KH-pH-CO2 chart and
was intrigued by the constancy of the pH drop for a given CO2 mg regardless
of the actual KH. iyswim.

Not having seen mention of this in my various internettings I thought I'd
ask for thoughts here
As you say, once a person is familiar with their KH changes (or lack of)
with time then both systems of targeting CO2 level would be good.

Since then a member has come up with the maths behind the constancy of the
pH drop for a given CO2 level across all KH values, so I am now happy that
I am not either mad or doing something wrong !

Regards.

wrote:
I found that if I wanted a 'target' CO2 level of 15mg/l this always
resulted in a drop of pH of about 0.7 from the no-CO2 equilibrium
(atmospheric) level for all KH values between 1 and 8

Am I losing my marbles, I've not seen any refs. on the internet to this,
they all require me to test the KH to know the mg CO2
What am I missing ?

Not everyone has a KH between 1 & 8?

On Thu, 12 Jan 2006 10:57:14 -0600, Rocco Moretti wrote:
Not everyone has a KH between 1 & 8?

I did not say that they would have.
That was just the range of values that I inspected.
quote (ie. all the KH's that I examined ) /quote
I was asking for clarification, not issuing a dictat.

Have you found a KH value where the constancy of the pH drop for a given
CO2 change does not hold true ?

This thread is interesting. Where can I go to get a copy of the chart
you are referring to?

http://www.aquatic-plants.org/articl...hph_table.html



Norm wrote:
This thread is interesting. Where can I go to get a copy of the chart
you are referring to?

Norm wrote:

This thread is interesting. Where can I go to get a copy of the chart
you are referring to?


If you prefer a Windows application that displays this chart and other
calculations useful for planted aquaria maintenance, then Chuck Gadd's
calculator is he

http://www.csd.net/~cgadd/aqua/art_plant_aquacalc.htm

--

Ptarmigan wrote:
On Thu, 12 Jan 2006 10:57:14 -0600, Rocco Moretti wrote:

Not everyone has a KH between 1 & 8?

I did not say that they would have.

Sorry, I wasn't trying to be snippy. I was trying to answer your
question, and the question mark was an indication of unsureness:

they all require me to test the KH to know the mg CO2
What am I missing ?

Not everyone has a KH between 1 & 8?

That was just the range of values that I inspected.
quote (ie. all the KH's that I examined ) /quote
I was asking for clarification, not issuing a dictat.

And I was trying to to point out that the situation *might* change for
someone with a higher KH. I have a KH in the 15-25 range, and a GH to
match. It's sometimes hard to remember that not everyone has liquid rock
for water. I was thinking you too might have gotten into the trap of
thinking that everyone has water like yours. So although such a
technique works for low KH waters, it might fail for higher ones, and
"what you're missing" is that the internet websites have to give advice
valid for all water types.

The question mark was not intended to be sarcastic or anything, it was
merely indicating the fact that I don't know if the relation breaks down
in high KH waters, and didn't have time to check when I posted.

Looking at http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm,
it appears you are correct, and KH doesn't matter - at any given,
constant KH, the pH drop of a given increase in CO2 is independant of KH.