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Question about pressurised CO2 and water disturbance

Yes, this is teaching me that measuring PH (even relative rather than actual) is better for me than a DC. I can see myself buying a PH controller quite soon.

I've also got the advantage of not having any fauna so minimal risk. Once I've got it stable then I will add some fish on a day I am in to watch them as the co2 kicks in and ramps up then adjust as necessary.
 
I've also got the advantage of not having any fauna so minimal risk. Once I've got it stable then I will add some fish on a day I am in to watch them as the co2 kicks in and ramps up then adjust as necessary.

Good idea. I am keeping a fish-less tank at the moment because I had many problems with a fluctuating BPS due to a bad needle valve. That is another biggie, the regulator. But even if you have a cheap one it can be made to perform great with a flow controller.

Here is someone using a pH controller if its of any interes:

http://www.ukaps.org/forum/threads/mountain-view.35570/#post-404150
 
I'll take a look at that tonight. No pictures load on the work network!

I have the co2art dual stage solenoid regulator. It wasn't their top one, but they suggested to to me as being better than most.
 
I have the co2art dual stage solenoid regulator. It wasn't their top one, but they suggested to to me as being better than most.

Ive got the cheap one stage one with the solenoid. Its impossible to get a constant BPS in my case. Im sure a double stage one is better though.
 
So you just open the needle valve fully then fit that inline before the bubble counter?

Thats what Ive done. But didnt really open the needlevalve all the way, but pretty sure thats what you should do. Its important to fix the little knob with the thread its got, once flow is set.
 
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Hi all,
What I'm getting here is that measuring ph with an electronic device is much more reliable than using a drop checker for measuring CO2, is that the general consensus? If that's the case then great, I like reliable accuracy and it's one less fiddly glass thingy hanging in my display! I've used a ph controller on my reef system but that was for running a calcium reactor and balancing KH which is quite a different kettle of fish
This bit is quite important, if you have very heavily buffered salt rich water (sea water is carbonate buffered and ~53,000 microS) then any pH meter will give you a fairly accurate measurement. As you move towards pure H2O (an electrical insulator) pH becomes both a less meaningful measurement, and much more difficult to measure.

You can't extrapolate from a buffered system (like Lake Tanganyika) to a much less buffered situation like the Amazon basin black (and clear) water rivers and lakes.

These problems come about because pH is a ratio, and "pH7" just means you have an equivalent number of H+ ion donors ("acids") and H+ ion acceptors ("bases"). It doesn't matter what that number is it could be 1:1, 10:10, 100,000:100,000 as long as it is a balanced equation.

This is also why pH can never be stable in very soft water, very small changes in the relative proportions of weak acids (like H2CO3) and weak bases (like O2) cause large changes in pH.
Provided you haven't contaminated the drop checker fluid it will be right and pH pen wrong.
This is also why "Ian_m" is right, pH meters are high maintenance bits of kit that need to be regularly calibrated (with pH buffers) and have their electrodes stored in a KCl solution etc.

They aren't "plug and play". If you are willing to spend a couple of hundred pounds on a pH meter/electrode combination, and have the time to buffer it before each use, it will give you an accurate and repeatable reading.

Drop checkers are accurate (<"read this thread">), and use the fact that carbonic acid (H2CO3) and bi-carbonate (HCO3-) are the weak acid and weak base pair in carbonate buffering.

Calcium carbonate is insoluble in water, but in water with carbonates present the small amount of CO2 (that goes into solution as H2CO3) is in equilibrium with the HCO3- to give a stable value of ~pH8 at atmospheric CO2 levels (400ppm CO2) and standard barometric pressure (1013mb).

When we add CO2 above atmospheric levels we drive the H2CO3 ~ HCO3- equilibrium towards H2CO3. We know that pH is a ratio, and that an acid is defined as a H+ ion donor and we've added extra H+ (from H2CO3), so the pH falls. How much the pH falls depends upon the reserve of carbonate buffering, we usually measure this as "dKH".

If we have a narrow range pH indicator ("bromothymol blue"), a solution made to contain 4dKH solution ("4dKH solution"), a drop checker with an air gap and a chart with experimentally derived CO2 levels for a range of pH values at a known carbonate hardness (below) it is a pretty robust system.
picture_1.png

cheers Darrel
 
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Wow, thats a detailed reply, and above my ability to comprehend in one go!

Darrel, you sound very competent on this topic, does my approach sound correct? Ultimately, I appreciate that I need to have my DC blue in the morning and Green (and stable green) when lights come on. I am using the PH pen as supplementary information to look at the relative drop.

I know I have hard water (how hard, I'm not sure, I only have basic test kits which I know are not accurate.) and that it has a naturally high PH (again, not sure exactly.) Based on this and the tables, I am not expecting to see a full PH drop, but I am still expecting my DC to go between blue and green once the correct amount of co2 is present in the system.
 
Here is someone using a pH controller if its of any interes:
This is also why "Ian_m" is right, pH meters are high maintenance bits of kit that need to be regularly calibrated (with pH buffers) and have their electrodes stored in a KCl solution etc. They aren't "plug and play".
This is why most people (there are exceptions, like the link you posted) using CO2 controllers either end up gassing their fish or adding no CO2 and growing algae. CO2 controllers (actually measuring pH) are high maintenance bits of kit where going out of calibration causes issues. Much better to not use CO2 controller and get your CO2 rate (bps) consistent every day and observe levels with drop checker and/or pH pen if you feel you need numbers rather than colours :D.
 
I agree with the veterans in here but will just add a couple of opinions.

1) If you look at most cases of people gassing their fish they are normally using a d.c. Most everyone Ive seen having algae issues use a d.c.
2) Normally we dont have KH under 4 in our planted tanks. Obviously this is a drawback of the pH method, but they all have drawbacks, and I think d.c. have more.
3) Also having high or low light makes a difference. If you want to have more control over your co2 a pH meter is a must. Otherwise, do you know someone other than T. Barr who adds more co2 to his tank without gassing his fish while monitoring with a d.c? Sorry but Im afraid none of us do. Even the best aquascapers in here. They use a d.c because thats what they learned with and they just adapt the light to need less co2, and theyve also learned to eyeball it etc.

Its all been said in that link Darrel added.
 
Hi all,
Wow, thats a detailed reply, and above my ability to comprehend in one go!
Water chemistry, and particularly buffering and pH, is quite a difficult area, which is why a lot of comment on the web isn't as informed as it should be. I'm not a CO2 user, mainly because I can find quite enough ways to kill my fish without adding another one.
Ultimately, I appreciate that I need to have my DC blue in the morning and Green (and stable green) when lights come on. I am using the PH pen as supplementary information to look at the relative drop.
Yes, you will just get less pH drop in harder water.
I know I have hard water (how hard, I'm not sure, I only have basic test kits which I know are not accurate.) and that it has a naturally high PH (again, not sure exactly.)
You should be able to get values from your water supplier.

The only hardness value you need to know accurately is that the drop checker solution is 4dKH.

Because the drop checker has an air gap, only CO2 will effect the pH.

Your added CO2 will continually out-gas (until dissolved CO2 levels equilibrate with atmospheric levels).

The CO2 that out gases into the drop checker will effect the pH (and the colour of the pH indicator), nothing else will. When you stop adding CO2, it will re-equilibrate with atmospheric CO2 levels and your drop checker solution will revert to ~pH8.

The lag in colour change occurs because gases are moving in and out of the drop checker via diffusion and the rate of diffusion will depend
upon the diffusion gradients between the tank water, air gap and 4dKH solution.

The steepness of diffusion gradients will depend upon the area of the gas exchange surface. This is why people have air pumps they turn on when the gas is off. A larger gas exchange surface will out-gas the CO2 more quickly.

cheers Darrel
 
Yes, you will just get less pH drop in harder water.

This is something I am very interested in Darrel. Hope you take your time to explain it to me as always:).

Harder water=higher Kh right?

The pH kH Co2 chart shows that "pH drop" is independent of the kH up to where Im concerned. If you do an example with two waters with different khs you will find this out. lets try:

Water 1: KH=2, Ph at the equilibrium with air=7.6(lets suppose we have 1.5 ppm of co2 and this shouldnt matter since both water will have the same rough co2 ppm in the equilibrium with air)
water 2: KH=5, Ph at the equilibrium with air=8( again lets suppose we have 1.5 ppm of co2 and this shouldnt matter since both water will have the same rough co2 ppm in the equilibrium with air)

Now lets look at the pH for both waters once we add 30 ppms of co2.
Water 1: KH=2, pH (at 30 ppms of co2)= 6.3
water 2: KH=5, (at 30 ppms of co2)=6.7

pH drop for water 1=7.6-6.3=1.3
pH drop for water 2=8-6.7=1.3

Same pH drop for two waters with different kH as to get the same co2 dissolved in them.
How can this be Darrel? Maybe the CO2 at the equilibrium with air is not the same? But then T. Barr would be wrong.

I used this chart which is more detailed but should be the same:
http://www.barrreport.com/forum/barr-report/co2-enrichment/11862-co2-ph-kh-table

I really believe here lies the core of the conflict. People say KH affects pH drop because it looks intuitive.
 
I did not verify it, but maybe it was meant to mean that to lower pH by CO2 supply in hard water you will have to add more CO2 (in volume) then to lower pH by the same value in soft water.
 
I did not verify it, but maybe it was meant to mean that to lower pH by CO2 supply in hard water you will have to add more CO2 (in volume) then to lower pH by the same value in soft water.

He (T. Barr) also states that you need approx the same ammount of co2 for both waters. He states that the solubility might be slightly different but it wont make a difference at all when adding co2, at least no a measurable difference. So you are right Ardjuna probably but this will not affect the "ph drop" .
 
Hi all,
This is something I am very interested in Darrel. Hope you take your time to explain it to me as always:). Harder water=higher Kh right?
The simple answer is I don't know.
but maybe it was meant to mean that to lower pH by CO2 supply in hard water you will have to add more CO2 (in volume) then to lower pH by the same value in soft water.
Yes, that is exactly what I had in mind.

"Harder water=higher Kh right?
" Intuitively that would be the reason, but as it is a buffered system I'm not sure. It wouldn't matter what dKH you started with, assuming all the hardness was via carbonates (and there weren't any acids other than H2CO3) then the pH would be ~pH8, whether it was 1 dKH or 20 dKH. Because of the small reserve of buffering at 1 dKH, you don't have to add much CO2 before you get a rapid fall in pH. Looking at the chart once you get above 4 dKH that relationship is more linear. I'm not a CO2 user, but there is an explanation in Ardjuna's thread <"here">.

CO2 is a bit funny because it exists as a dissolved gas and as an acid, and carbonic acid (H2CO3) is "diprotic" - it has two H+ ions, so it has 2 disassociation constants.

All the chemistry "bits" are here, but the chemistry is beyond me: <http://lawr.ucdavis.edu/classes/ssc102/Section5.pdf>.

cheers Darrel
 
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Thanks Darrel. I appreciate it.

"Harder water=higher Kh right?" Intuitively that would be the reason, but as it is a buffered system I'm not sure. It wouldn't matter what dKH you started with, assuming all the hardness was via carbonates (and there weren't any acids other than H2CO3) then the pH would be ~pH8, whether it was 1 dKH or 20 dKH. Because of the small reserve of buffering at 1 dKH, you don't have to add much CO2 before you get a rapid fall in pH. Looking at the chart once you get above 4 dKH that relationship is more linear

Maybe the chart is not very accurate. I understand other acids/bases/buffers play a role here, but if we want to see the effects of kH then we need an experiment with only KH(carbonates/bicarbonates/ Na2CO3?) + CO2 + pure H20. This is supposedly what the pH/Kh chart is right? And in the more detailed chart it looks like no matter what KH the ph drop is the same for a certain co2 ppm and starting with the same equilibrium. I've tried with the lowest value and also with the highest. Maybe the chart is just a formula which doesnt represent reality for all khs?

I understand people might think I'm overthinking this but this makes a difference IMO.

I can just say that I've had a pH drop of 1.1 in my tank without gassing my fish, but this water is possibly all carbonates. It would be nice to show what happens in waters with other buffers in it. This tank has a high KH of around 18 possibly. And its seems Toms experience shows the pH drop varies from 1.1 to 1.4 normally. So I might be wrong but we have a range here of 0.3 ph units of unknown. Its not that much if you think you can add co2 up to a ph change of 1 without risks (well not too many anyway).

Anyways, all I can say is that it remains a matter of opinions for now.
 
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Hi all,
Jose I'll ask a colleague who is a chemist. But I think I've got it.

Assuming that the "pH drop of 1" for ~30ppm CO2 is right, it is because it is a buffered system, and pH is a log10 scale. The drop in pH is determined only by the concentration of CO2 in the water.

In the same way a reserve of HCO3- (dKH) will maintain pH at ~pH8 at atmospheric CO2 levels, as you increase the CO2 levels you drive the equilibrium towards H2CO3 and the pH falls.

Assuming you still have a reserve of buffering then the fall in pH may appear to be linear (exponential data plotted as log10 values will form a straight line).

I think everything starts from the assumption that water in equilibrium with atmospheric CO2 levels contains ~3ppm CO2. A drop of 1 pH unit is actually an increase of 10 in the ratio of H+:O-H ions, when you have a pH drop of 1 unit you have:

3ppm x 10 (1 as log10) = 30ppm CO2.

This is from <"The Planted Tank">
But what I was saying, about the derivatives, if what hoppy was saying is correct, then that means that change in pH (Y) is a function of change in KH (X) (X change in KH results in Y change in pH). This means that the derivative of this function (dy/dx) is independent of CO2. This does not mean that the variable of pH (Y) itself is independent of CO2. If it was, then (dy/dz) would be zero, meaning that CO2 would not affect pH. So, pH has some sort of relationship with CO2 (Z) a very complex one. pH (Y) is dependent on both pH and CO2, but dy/dx and dz/dy are independent of each other.

Ok, hold on, based on what hoppy said, the equation is Z/Zo=10^(Yo-Y) which means Z=Zo[10^(Yo-Y)]
so to calculate CO2(Z), you plug in starting ph for Yo, and current pH for Y and I guess we are assuming that the starting CO2 is 3ppm?
This also looks an understandable link <http://institutebishop.org/enviro_11.pdf>.

cheers Darrel
 
Assuming that the "pH drop of 1" for ~30ppm CO2 is right, it is because it is a buffered system, and pH is a log10 scale. The drop in pH is determined only by the concentration of CO2 in the water.

In the same way a reserve of HCO3- (dKH) will maintain pH at ~pH8 at atmospheric CO2 levels, as you increase the CO2 levels you drive the equilibrium towards H2CO3 and the pH falls.

Assuming you still have a reserve of buffering then the fall in pH may appear to be linear (exponential data plotted as log10 values will form a straight line).

I think everything starts from the assumption that water in equilibrium with atmospheric CO2 levels contains ~3ppm CO2. A drop of 1 pH unit is actually an increase of 10 in the ratio of H+:O-H ions, when you have a pH drop of 1 unit you have:

3ppm x 10 (1 as log10) = 30ppm CO2.

See? I wouldnt have said it in a million years, even though I think I understand it cause Ive done some chemistry in the past:lol:.

So just to recap Darrel. Could we conclude that "pH drop" is independent of KH? Even if its not exactly 1 unit of ph. In other words you need the same pH drop no matter the hardness of the water. Now there are also other acids/bases. And this is another big question. Is it still the same pH drop if we add an acid that? I think it is because it will break down KH. And is it the same pH drop if we add a base? Dont know.
 
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