# Drop checker color relation to KH question



## HiNtZ (10 Sep 2016)

I don't know how to word the title, this has been confusing the life out of me since it dawned on me today.

If I have a drop checker with 4dKH solution, and I have 4dKH tank water, the nice solid green I see means I'm round about what, the 33ppm range (as an example anyway), let's just say "the perfect range" regardless of the number.

Ok - bare with me. So when I have 4dKH solution in the DC, and say 6dKH tank water and the DC is reading that solid green.... that's not at that same "range"? Is it? O mean, it's still green saying everything is mint, but really, the reality is I'm actually under, or is it over that range. I can't decide which way but there's the scenario.

Now let's say that my DC is 4dKH and my tank IS 6 dKH, does a more yellow DC still mean I'm still within the "perfect range" (not above) or is there some complex relationship (i.e Voodoo/black magic) with the PH and actual KH of the tank that makes the DC green indicating "the perfect range", as it were?

Does that make sense? ....it doesn't to me


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## kadoxu (10 Sep 2016)

Well... I'm still waiting for my first CO2 system ever to arrive, but I've been reading a lot about it in the past week or so... so take my explanation with some caution.

So, starting with the basics
The Drop Checker (DC) solution in nothing more than a PH test, changes in the solution color means the solution's PH changed. 
The higher the KH, the harder it gets to change the water's PH. KH affects the amount of CO2 needed to change the solution's PH level. (I think CO2 is acidic, so correct me if I'm wrong, please). A higher KH means a better buffering capacity, making PH changes harder.

The DC solution measures roughly the CO2 levels in the tank by roughly showing you the solution's current PH in a specific colour (like when you use a test kit). Change the amount of  CO2 in the tank, and the PH in the solution will change (and changes colour), again, more CO2 -> lower PH, less CO2-> higher PH.

I believe that the use of a 4dKH solution in the DC, makes the DC usage a standard for everyone, so it doesn't matter if your tank water is 9dKH, 6dKH or even 15dKH, you can roughly compare CO2 saturation in two different tanks. This means that if you use a different solution in the DC, the colour changes will not happen the same way.

To summarise, speaking strictly about CO2 levels and to answer your question... your tank water's KH doesn't affect the CO2 measurement made in the drop checker.


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## zozo (10 Sep 2016)

The drop checker works regardles from your tankwaters kh, the co2 in your water column gasses out into the dropchecker and mixes with the dkh4 water in the DC and changes it's ph, the bromothymol in the water from the DC will change color. Green means there is about 30ppm co2 in the drop checker.. The co2 in the tank and in the dropchecker always balance out and are fairly the same, they exchange this gas with eachother constantly via that bubble of air betweem them. This process only takes some time, if the co2 in the tank drops it will gass out less co2 into the DC and the co2 level in the DC water will drop as well, the same thing happens if the co2 level in the tank rises, it gass out more co2 into the DC. The water can never gass out more or less co2 into the dropchecker than it has in itself, in the end they always equal out the same.

The only thing which isn't always the same is the Dkh value of tank water and water in the DC.. In the DC it is a static 4dKh and doesn't change, because there is nothing in there that can change it.. In the tank this is different, there are substrate hardscape, fish and plants and tap water wich can have effect on the Kh. The co2 level has effect on the pH. So if you have a different kH level you will have a different pH level with the same amount of co2 in it.

Since dKh4 water with 30ppm co2 is green with a +/- pH6.6 in the DC can result in a pH 6.8 in the tank if it has a dKh6..  which has a slightly different color green if you would do a bromothymol pH check on your tank water. But the co2 level is fairly the same.

We want to use dKh4 in the DC because of the static relation betweem color and co2 level, like a standard value.. We thrive to have that 30ppm.. So this doens't mean if you don't have 4dKh in your DC that it doesn't work.. It still works the same only the color at 30ppm wont be the same. But if you find out which color relates to 30ppm co2 you can have any dKh value in your DC as well.

Manuel lately posted a nice graph about that you could use as a reference for that.  See point 3 at the description bellow the chart..


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## Manuel Arias (14 Sep 2016)

Both previous answers are fully correct. These tables are only valid for the drop checkers and they cannot be used with external measurements for a few reasons:

-KH in aquarium will be affected by much more things than only (bi)carbonates. As result of that, KH measurement from tank water will be misleading. Drop checker, however, is filled with a solution in which all the alkalinity is due to (bi)carbonates, so the issue does not exist in them.

-pH changes in aquarium will also be due to many factors, not only CO2 injection. Again, this is not the case in the drop checker, in which the gap between solution and water prevents this to happen. Only changes in CO2 levels affect to pH in drop checker.

-Aquarium is an *open system with atmosphere*, which means that CO2 in water looks for equilibrium with atmosphere. As result of that, CO2 levels using these kind of tables for direct measurements *are wrong*, because the theory behind these computations assumes that you have stable concentrations of CO2 in water that can be larger than the equilibrium. This is true meanwhile you inject CO2, because your driver of concentration is the injection, but once you stop doing so, water of aquarium starts to lose CO2 until reaching equilibrium with the air, (i.e. about 0.5 ppm, as determined by Henry's Law, no 3 ppms as some people defend). On the other hand, the drop checker acts as an *open system with the aquarium* so the levels of the gas in the drop checker are actually matching the values of the table all the time, as there is no direct influence of atmosphere.

So when using the drop checker, you need only to know the dkH in the drop checker and the color. Even if looking at colors can be difficult, this is only the real technique that works. Rest of ideas you see around are just proxies which are much affected by third factors. As well pointed out by Marcel, this information is useful if you wish to aim different CO2 levels. The 30 ppm value is a rule of the thumb, but a planted aquarium with low demanding plants (or low density of plants) and 30 ppm could develop algae due to an imbalance of nutrients consumption, light and CO2 levels.
For instance, in the table, if you want to have the green colour corresponding to 20 ppms of CO2 instead of about 30, you just need to change the kH of the drop checker to 3 dkH. This, however, requires to get indicator with no prefixed dkH solution, but that is relatively easy to get (there are a few brands selling it). It also require you to prepare your own kH solution. The same site, from what the table comes, explains also how to do so.

Cheers,
Manuel


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## dw1305 (14 Sep 2016)

Hi all, 





Manuel Arias said:


> i.e. about 0.5 ppm, as determined by Henry's Law, no 3 ppms as some people defend


 I've wondered where the 3 ppm came from as well. I think the level will be higher than the <"theoretical ~0.5 ppm CO2">, mainly because the air in a room has more CO2 than the atmospheric level (of 400ppm). 

We have a CO2 monitor in the lab. and it usually reads at 600 - 800ppm CO2. 

cheers Darrel


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## HiNtZ (15 Sep 2016)

Manuel Arias said:


> This is true meanwhile you inject CO2, because your driver of concentration is the injection, but once you stop doing so, water of aquarium starts to lose CO2 until reaching equilibrium with the air, (i.e. about 0.5 ppm, as determined by Henry's Law, no 3 ppms as some people defend).
> 
> Cheers,
> Manuel



So this is why it's generally thought that PH controllers do more harm than good?

Great explanation by the way.


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## HiNtZ (15 Sep 2016)

dw1305 said:


> Hi all,  I've wondered where the 3 ppm came from as well. I think the level will be higher than the <"theoretical ~0.5 ppm CO2">, mainly because the air in a room has more CO2 than the atmospheric level (of 400ppm).
> 
> We have a CO2 monitor in the lab. and it usually reads at 600 - 800ppm CO2.
> 
> cheers Darrel



Is that how much is naturally in the air around us??? That's a massive difference to in tank.

No wonder the plants pearl like mad after a water change where they were exposed to atmosphere - even if for a few minutes.

This hobby never ceases to amaze me as to what we are actually up against to maintain the perfect ecosystem.


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## zozo (15 Sep 2016)

HiNtZ said:


> So this is why it's generally thought that PH controllers do more harm than good?
> 
> Great explanation by the way.



This could be personal experience where some things probably where overlooked and a ph controller wasn't the best choice for this type of setup. Or thought a ph controler is a laid back intelligent device which does all the work for you. Well that's not the case it isn't  there are some safety issues we need to take into consideration.. as any other device in your tank they need to checked regularly and you still beter use a dropchecker.. It's the same as with the heating, which has a thermostat, but still you use a thermometer to double check.

The thing is as already sayd, there are several substances which could lower or rise a ph value in the tank water. And a ph controler does measure this ph and accordingly does add co2 or not to the tank via the solinoid which is controlled by it.. Thus if something like acids coming from what ever source is lowering your ph the controller will react as if it was co2 and stops adding it.. That is theoreticaly a very good point after all it's a ph meter and not a co2 meter as is the DC.. The DC will react solely on co2 and the ph controller on ph.

Tho if it's practicaly such a good point depends on some external factors which someone should know and be able to anticipate to.. If there are substances in the tank or added to the tank then the aquarist in situ should know this on forehand and than it's his fault to choose for a ph controler in such a setup. Substances lowering the ph do not fall from the sky and also do not drasticaly happen over night.. If it does there is something seriously wrong and already long before it suddenly happened. Ph controller can be susceptible to electrical interferance if placed incorrectly, this is something you should know before using it and if not you will notice soon enough with daily double checking.

I'm using a ph controller already for over a year now to control my co2 and also have a dropchecker in the same tank.. So i can double check all the time and i do.. And as long as i'm using them there wasn't a day where one of them was off, both stayed in a rock solid same range.. Stable ph in the tank with a stable same color in the DC.
I thought about it a lot and i know my tank and i know what's in there and what it is doing.. And i can think of nothing which could all of a sudden change my ph value in such a drastic manner so the ph controller becommes unreliable.. I've even asked the question here at ukaps in topics where the issue came up.. What in gods name would and could do that without me noticing it or doing it myself?? I din't got an answer to it..

If there are ph changes they will be rather tiny and not realy influencing the co2 that much it becommes a problem over night. It could change over longer periodes of time and then the controler needs to be adjusted accordingly. If you don't you might run in to problems one day.

Personaly i only experience benefits with the ph controller.. It keeps my co2 level rock steady even if the bubble count fluctuates it doesn't matter.. Even if it fails to chut off, my bubble count is set in such a way it will never ever gass the tank..

99% of the bad experiences with these devices are human error and ignorance.. Ph controllers only harm your bank account, good ones are realy expensive and you could easily do without.. But if you have the cash to spend to spoil it on the little benefits they can bring.. It's up to you..


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## dw1305 (15 Sep 2016)

Hi all,





HiNtZ said:


> No wonder the plants pearl like mad after a water change where they were exposed to atmosphere - even if for a few minutes.


Yes, that is partially why I'm so keen on floating or emergent plants, they have Diana Walstad's <"aerial advantage">.


HiNtZ said:


> Is that how much is naturally in the air around us??? That's a massive difference to in tank.


 The atmospheric level of CO2 is ~400ppm, up from ~280ppm before the industrial revolution and still rising rapidly.





Carbon dioxide is a soluble gas, but its concentration is dependent on <"Henry's Law"> (below). 





> ...the mass of a dissolved gas in a given volume of solvent at equilibrium is proportional to the partial pressure of the gas.


 As Manuel noted earlier at atmospheric CO2 levels (but this is actually worked out for 340ppm CO2? Manuel?) you only end up with 0.44ppm dissolved CO2.





Manuel Arias said:


> Below 5 atm of pressure, Henry's law applies and concentration of CO2 is: [CO2] (mol/l) = 0.032*PCO2. PCO2 is equal to 10^(-3.5) atm, so [CO2] = 10^(-5) M. This, translated to mg/l = 0.44, so *0.44 ppms*. This is the maximum concentration, in pure water, that you can achieve, considering 25 degrees of temperature.


 If you have higher CO2 levels the partial pressure of the gas is increased and more CO2 goes into solution.

You can work it out for any atmospheric CO2 concentration from (this is for 387 ppm CO2):
[CO2] = P/KH = 3.87 x 10-4 atm/29.41 atm M-1 = 1.32 x 10-5M = 0.58ppm ((1.32*10-5)*44)

For 800ppm CO2 I think that equates to 1.04ppm CO2, so still a long way short of the 3ppm figure.

The 44 is the RMM of CO2 (C=12, O=16). One Mol. of CO2 is 44g.

cheers Darrel


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## HiNtZ (15 Sep 2016)

zozo said:


> after all it's a ph meter and not a co2 meter as is the DC.. The DC will react solely on co2 and the ph controller on ph.



That's probably the best and most simplest explaination I've ever heard, and it has got me thinking! Which gets me thinking....... is there such a device that is a combination of PH controller and drop checker? By that I mean rather than the PH controller testing the PH of the tank (which as you said is open to fluctuations for whatever reasons), could it not test the PH of the DC fluid or something along those lines to stop the CO2 control being based of a fluctuating tank value and being based instead on something stable and real like the DC?



zozo said:


> Ph controller can be susceptible to electrical interferance if placed incorrectly, this is something you should know before using it and if not you will notice soon enough with daily double checking.



You know, I'm glad you pointed this out. I've seen a couple (read literally as only 2) videos online where people have questioned the erratic behavior of their PH controller due to electrical interference from say an inline heater, or a separate temperature probe or whatever when in the water. This alone put me right off using one, even though I was so excited to have been given one for free.




zozo said:


> I'm using a ph controller already for over a year now to control my co2 and also have a dropchecker in the same tank.. So i can double check all the time and i do.. And as long as i'm using them there wasn't a day where one of them was off, both stayed in a rock solid same range.. Stable ph in the tank with a stable same color in the DC.



So what are you trying to say here? Are you using it solely as a reference and perhaps an emergency cut off rather than a regulator (where it would otherwise be constantly on and off throughout the day)?



zozo said:


> If there are ph changes they will be rather tiny and not realy influencing the co2 that much it becommes a problem over night. It could change over longer periodes of time and then the controler needs to be adjusted accordingly. If you don't you might run in to problems one day.



I see a 0.4 ph rise (from 6.4 to 6.8) during the 9.5 hours the CO2 is off - I thought that was pretty decent. What is your opinion on this?



zozo said:


> 99% of the bad experiences with these devices are human error and ignorance.. Ph controllers only harm your bank account, good ones are realy expensive and you could easily do without.. But if you have the cash to spend to spoil it on the little benefits they can bring.. It's up to you..



Opinions on the JBL 12V?



Thanks, great replies - much appreciated.


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## HiNtZ (15 Sep 2016)

dw1305 said:


> Hi all,Yes, that is partially why I'm so keen on floating or emergent plants, they have Diana Walstad's <"aerial advantage">.  The atmospheric level of CO2 is ~400ppm, up from ~280ppm before the industrial revolution and still rising rapidly.



Great chart, saving that! Thanks!



dw1305 said:


> You can work it out for any atmospheric CO2 concentration from (this is for 387 ppm CO2):
> [CO2] = P/KH = 3.87 x 10-4 atm/29.41 atm M-1 = 1.32 x 10-5M = 0.58ppm ((1.32*10-5)*44)
> 
> For 800ppm CO2 I think that equates to 1.04ppm CO2, so still a long way short of the 3ppm figure.
> ...



I'm not going to pretend for a minute I understand that, so I will not rest until I do. Really wish I'd paid more attention in maths and science :/


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## Manuel Arias (15 Sep 2016)

HiNtZ said:


> So this is why it's generally thought that PH controllers do more harm than good?
> 
> Great explanation by the way



Yes, that's right. The theory of the drop of pH in 1 unit is mainly bullshit (see below). I am glad you found it useful. 



dw1305 said:


> I've wondered where the 3 ppm came from as well. I think the level will be higher than the <"theoretical ~0.5 ppm CO2">, mainly because the air in a room has more CO2 than the atmospheric level (of 400ppm).
> 
> We have a CO2 monitor in the lab. and it usually reads at 600 - 800ppm CO2.



Hi Darrel,

You are right in that sense. CO2 in a room can be higher, but still, 700 ppm are about 1 ppm of CO2 in equilibrium with water, far beyond from the claimed 3 ppm.

I have been doing some work in the last weeks about CO2, and I got where the problem is coming from. Essentially, the 3 ppm story comes from two (wrong) assumptions:

a) Most tap waters have an alkalinity close to 18 dkH.
b) The carbonates equilibrium does not involves exchanges with atmosphere.

The assumption (a) could have been true many years ago in some areas. Nowadays, many people use RO, or mix of RO and tap water, and most people focused in planted tanks seems to go towards soft water strategies rather than hard waters. However, even if this was not true, assuming most waters have 18 dkH is just very simplistic and then, wrong.

The second assumption is also quite worrying. There is a huge difference, when computing the equilibrium, between considering that there is not CO2 exchange with atmosphere and when there is some. The results of 3 ppm just comes from assuming that CO2 concentration is in fix equilibrium with the alkalinity.

For instance (embrace yourselves, some equations are coming), the carbonates equilibrium has mainly four stages:

1. Dissolution of CO2 from air into water, which is determined by Henry's Law and roughly estimated as:

[CO2]d = PCO2(air) * 10^(-1.43).

2. Conversion of dissolved CO2 into carbonic acid by combination with water molecules

CO2(d) + H2O <==> H2CO3.

Only a small amount of dissolved CO2 becomes into carbonic acid. More specifically, [CO2](d) = 650*[H2CO3], so very few molecules. However, conversion to carbonic acid is so fast that any secondary reaction reducing H2CO3 means that more CO2 dissolved in water is taken to compensate the loss. In practical terms, all the dissolved CO2 can then be considered as carbonic acid, common practise in this kind of equilibriums. In this way:

[CO2](d) + [H2CO3] = [H2CO3*],

being [H2CO3*] the term used in the carbonates equilibrium.

3. Part of the dissolved carbonic acid releases protons to water, becoming into bicarbonate:

[H2CO3] <==> [H+] + [HCO3-]

The generated protons reduce the pH what reflects the acidic effect of dissolving CO2 in water. As usual in equilibriums, molecules of carbonic acid are splitting and recombining all the time. However, in balance, there is certain amount of it always split, which is determined by an equilibrium constant, K1:

[H+]*[HCO3-] / [H2CO3*] = K1

As K1 remains fixed, the amount of bicarbonates depends on pH and concentration of dissolved CO2:

[HCO3-] = K1 * [H2CO3*] / [H+]

What means that at higher pHs, the amount of dissolved bicarbonates, for the same concentration of CO2, increases. And the other way around.

4. However, this is not the end of the story. Part of the bicarbonates also disassociates generating protons and carbonates:

[HCO3-] <==> [H+] + [CO3(2-)]

In the same way than before, the process happens in both directions all the time and there is certain amount of carbonates what is expressed through an equilibrium constant, K2:

[H+]*[CO3(2-)] / [HCO3-] = K2

Then, amount of carbonates is determined by the pH and the amount of bicarbonates existing in water:

[CO3(2-)] = K2 * [HCO3-] / [H+]

Again, by increasing the pH we increase the concentration of carbonates and vice versa.

Now, all these expressions relates the carbonates equilibrium. By itself it is impossible to solve, as CO2 dissolving in water changes pH and [H2CO3*] at the same time, so it is not possible to solve the equations. This is where alkalinity plays a role. Alkalinity, TA, is the estimation of the capability of water to absorb protons. In pure water, with all the alkalinity due only to carbonates and bicarbonates, the expression is:

TA  = [HCO3-] + 2*[CO3-] + [OH-].

If we assume that the expression of TA is correct, then our value of KH in water is just due to these species, and hence, we can use the value in dkH to determine TA, and then having the answer. This requires some numbers. Let's asusme that we have the wrongly considered standard 18 dkH. Now, dkH are german carbonate hardness degrees, which are expressed as equivalent to 17.848 mg/l of CaCO3 dissolved in water. This means that our water, with 18 dkH is equivalent to:

[CaCO3](d) = 17.848 (mg/l) * 18 = 321.264 mg/l

To translate this to other carbonated species, we need to become this into mols, which is done using the CaCO3 molecular weight, i.e. 100.0869 gr/mol. Doing so:

[CaCO3](d) = 321.264 (mg/l) / (100.0869 (gr / mol) * 1000 ( mg/gr) = 0.00321 mol

We need to be, however, a bit careful about the value, as it relates to the alkalinity generated purely by carbonates, i.e. after converting all bicarbonates into carbonates. Expression of TA then needs to be readjusted:

TA = 2*[CO3(2-)] = 0.00321 * 2 = 0.00642 M

Reason why we can do this is because a mol of CaCO3 is equivalent to a mol of CO3(2-). However,  [CO3(2-)] is not going to be such value, so still we need to make some approximations. To solve the issue, we can assume that alkalinity has been mainly originated by dissolution of carbonated rocks by acidic attack of rain, which is a fair assumption in most fresh water environments. Then:

CaCO3 + H2O + CO2 = Ca + 2 * HCO3-

This means that resulting concentration of bicarbonates is equalt to two times the concentration of original carbonates. This matches with the value of TA, and then:

TA = [HCO3-] = 0.00642 M

So, now, with this assumption, we have then the resulting concentration of bicarbonates. This, translated to ppms and using the molecular weight of bicarbonates:

HCO3- = 61.01 gr/mol

*[HCO3-] = 0.00642 (mol/l) * 61.01 (gr/mol) * 1000 (mg/gr) = 391.68 ppm*

Next step is to find out pH, so we can find the value of dissolved CO2 and the value of carbonates in equilibrium. To do so, we need to use the expression of proton balance in water when dissolving bicarbonates salts:

[H+]total = [H+]water + [H+]carbonates - [H+]carbonic acid

The total of protons is equal to the ones found in pure water plus the ones generated by dissociation of bicarbonates into carbonates, minus those one absorbed by bicarbonate ions to form carbonic acid. We can now put this in terms of existing variables. For instance, in pure water:

[H+] * [OH-] = 10^(-14) = KW

This is known as ionic product of water, which reflects the equilibrium between protons and hydroxide ions. In pure water, with a pH = 7, [H+] is equal to [OH-]:

[H+]  = [OH-] = 10^(-7)

This means that [H+]water can be replaced by [OH-] as the value is the same. Additionally, we can work the expression to get the value of [OH-] as function of [H+]:

[OH-] = KW / [H+]

Furthermore, from the equilibrium it is clear that

[H+] carbonates = [CO3(2-)]

[H+]carbonic acid = [H2CO3*]

This is true because, in both cases, converting bicarbonate into carbonate or carbonic acid just involves the transfer of a single proton with water. Now, replacing terms in the proton balance equation:

[H+] = KW / [H+] + K2 * [HCO3-] / [H+] - [H+] * [HCO3-] / K1

We have now one equation and a single unknown, the [H+] concentration. Working in the algebra of the expression, we can put in one side all the references to protons, getting the expression:

[H+] =( (KW + K2 * [HCO3-]) / (1 + [HCO3-] / K1) )^0.5

K1 and K2 are equilibrium constants. Their value is rather imprecise and in fact is difficult to tell which ones must be used. However, traditionally in the hobby, the following values apply:

KW = 10^(-14)
K1 = 10^(-6.3)
K2 = 10^(-10.33)

And with [HCO3-] = 0.00642, we can solve the equation and get [H+]:

[H+] = 4.9215 * 10^(-9) M

that translated to pH as
*
pH = -log10([H+]) = 8.31*

Having [H+], we can now determine the amount of dissolved CO2, as

[H2CO3*] = [H+] * [HCO3-] / K1 = 6.304 * 10^(-5) M

As molecular weight of CO2 is roughly 44.01 gr/mol and ppms is passed to mg / l:

*[H2CO3*] = 6.304 * 10^(-5) (mol/l) * 44.01 (gr/mol) * 1000 (mg/gr) = 2.77 ppm = ~ 3 ppm.
*
So, it is from these computations where the value of 3 ppm comes, by assuming that most water has 18 dkH.

The associated concentration of carbonates (to complete the equilibrium), will be then:

[CO3(2-)] = K2 * [HCO3-] / [H+] =  6.102 * 10^(-5) M

And this translated to ppm:

CO3(2-) = 60 gr/mol

*[CO3(2-)] =  6.102 * 10^(-5) (mol/l) * 60 (gr/mol) * 1000 (mg/gr) = 3.66 ppm
*
The interesting part, and source of the error, is considering that the obtained [H2CO3*] value will not change and then, CO2 will remain in water, which allows to get about 3 ppm of CO2 when KH = 18 dkH. This is totally false. By Henry's law, as pointed out, maximum concentration *in equilibrium* would be:

[H2CO3*] = 10^(-3.5) * 10^(-1.43) = 1.1749 * 10^(-5) M, which is equivalent to

*[CO2](d) = 1.1749 * 10^(-5) (mol/l) * 44.01 (gr/mol) * 1000 (mg/gr) = 0.52 ppm = ~0.5 ppm
*
The key of this part is the words "in equilibrium", which means that enough time has passed since the addition of the bicarbonates to generate a solution of 18 dkH. The full chain is as follows:

a. Dissolution of the carbonated rocks by acid water from rain produces the bicarbonates, which dissolve in water very fast.
b. The resulting bicarbonates look for equilibrium, fixing pH of water and generating certain amount of carbonate ions and certain amount of dissolved CO2, in a relatively fast process.
c. However, dissolved CO2 are higher than the maximum values associated to the equilibrium with the atmosphere. This means water starts to lose CO2 to the air.
d. The degasification ends when CO2 dissolved in water equals the value in atmosphere. This process does not affect to alkalinity because the loss of CO2 produces more carbonates as bicarbonates disappear due to the change of pH. However, pH increases in the process, so degassed water will have higher pH than solution before the equilibrium is reached:

Note that, the loss of CO2 implies consuming protons and bicarbonates:

HCO3- + H+ <==> CO2 + H2O

As protons are consumed, pH increases and system displaces towards carbonates generation.

It is possible to get the final output for this situation and getting the species in the new equilibrium and pH after degasification, but that is a bit long for now. However, I wanted to show that the assumption of KH = 18 dkH and 3 ppm in water is rather arbitrary and doe snot obeys at all to real science associated to the problem, as most natural waters are indeed in equilibrium with air, i.e. changes in alkalinity are affecting to pH but not much to the CO2 concentrations. There are exception, of course, as waters coming from hydro-thermal processes ending in rivers/lakes before degasification is completed, or local processes like high concentration of organic matter being degraded, or water coming out from karst systems underground. But as a general rule, if no CO2 injection is produced by other means, natural water has 0.5 ppm of CO2 (considering a PCO2 of 350 micro-mol, obviously).

Cheers,
Manuel


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## Manuel Arias (15 Sep 2016)

dw1305 said:


> As Manuel noted earlier at atmospheric CO2 levels (but this is actually worked out for 340ppm CO2? Manuel?) you only end up with 0.44ppm dissolved CO2.



Yes, that's right, Darrel. I used the standard value assumed in Chemistry, but being honest, this should be updated, as CO2 levels are far beyond that, nowadays. This is why ocean acidification is a problem: Increasing CO2 levels in air propagate to ocean water, reducing pH, what affects to the carbonates equilibrium, reducing the omega point of organic carbonates formation. As a result, inverts have a hard life to produce shells, and more importantly, diatomea have the same issue. This strongly affects to the carbon pump driven by microalgae that allows oceans to absorb more carbon from air. The process is then a loop that reduces more and more capacity of oceans to absorb CO2 and at the same time can kill many species relying in shells.

Cheers,
Manuel


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## zozo (15 Sep 2016)

What very few people are aware of is that electrical devices in your tankwater can leak a current.. This can be an induction current cuased by a magnetic field induced by the coild wires and the magnet in the pumps used. Or in the worst case a water leak in the housing froma pump or a heater, this can be the caue of having an electrical current in the tankwater. As long there is electrical resisntance enough so to fuse doesn't blow there will be current in the tankwater. Usualy not an issue as long as the tank water isn't grounded.. If it's just a glass canister with a body of water the current can not flow and cause no harm.. As soon as it is grounded the current starts to flow through the tank and cause harm and even sick fish because they have a constant current flowing through their body. Evrybody should check this once in a while, whit a multimeter, throw the possitive lead in the tank and hold the negative lead to a grounding source, near by heating pipe of the house whatever as long it has ground. Then you'll measure the voltage leaking into your tank water. A few milivolts is normal and probably caused by the pumps induction.. But i've red articles where people measured 36 volts fluctuations in their water in several corners of the tank. Now thats a major leak and time to replace a pump or a heater.

Especialy those titanium heaters are often the culprit, these heater if forgoten to pull the plug during a water change will heat up very rapidly and burn the rubber seal from the plastic cap where the thermostat is situated. If after that fully submersed again your good to go and powering the tankwater too.. Glass heaters if you forget to unplug these they crack completely open if the tank is filled with cold water again. Titaniums do not show physical damage other then power leakage.

Now a PH meter is a volt meter, i wont go into detail but that is how it measures ph, the voltage difference between the 2 probes in th penn. A permanent ph eter connected to the power grid needs in the same time functions as a ground penn, because the pen is powered and connected to a pcb wich is again connected to the power grid via the powersupply. So if there is a power leak into the tankwater it will start flowing to the ground via the PH meter and probably infuence it's readings. Magnetic induction from a power head near the probe can also cause false readings. Several household devices near the meter can cause it.. Ph meters should always be placed as far away as possible from electrical devices.

(little side note to the story is, glass is an insulator, if there is a power loss in the tank it will only be an issue if it is grounded.. So if you happen to use a ground penn and happen to have a leak not enough to blow the fuse. You are not helping your fish you more likely make them sick.. Think twice, why you use them.. They are not what they are solled for.. Its a hoaks and a waste of money, throw them away as far as you can. Tanks should never be grounded. Electrical equipment should be chacked regularly do not leave your faight in the hands of a ground penn).

And yes i use the ph controller to regulate the co2, that's what it's made for and it does this with a preset ph value.. But i also use a drop checker to double check. After all it's a electrical computing device which always can give up you just never know. Till now it didn't, but still anything automated can fail at one time or another that's just a fact. But if it fails it can never put to much co2 in the tank, because my bubble count is set witht he help of the drop checker. So if it fails to shut off the co2 i will never reach a dangerous level. My main reason for using it, was the buble count fluctuations, these were in my case not stable, could be the needle valve or the regulator, hence i do not know i happen to have a PH controler, this prevents these fluctuations. My critical point is ph 6.2 where i become yellow, my ph controler preset is ph 6.9 and my dropchecker is green. So i the benefit i experience from this controler it keeps the co2 level steady with not using it i would be affected with fluctuations in co2 because of an unstable bubble count. It aslo prevents me from the need to invest in a beter regulator or needle valve, without actualy knowing if a new one would solve it. But why should i change a winning team or repair whats not broken.

The ph rise you experience during co2 off time is normal, thats the degassing of the water. Everybody has..  Even a low tech does that, but then the other way around, dropping during the night and rising during the day.

I do have no opinion on the jbl i have a Milwaukee and a Hanna. I was lucky to have found them used for a fair price and i'm happy with them. I would probably not be as happy if i had to buy them for a new price.


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## dw1305 (15 Sep 2016)

Hi all, 





Manuel Arias said:


> I have been doing some work in the last weeks about CO2, and I got where the problem is coming from. Essentially, the 3 ppm story comes from two (wrong) assumptions:


 Thanks Manuel, I think I can follow that.


Manuel Arias said:


> Alkalinity, TA, is the estimation of the capability of water to absorb protons


 I like the <"Bronsted Lowry"> explanation of bases and acids as "proton acceptors" and "proton donors" respectively, it makes it easier (for me) to understand why compounds are acidic, neutral or basic in solution.

I'm also aware of the DIC Bjerrum plot equations for carbonate system, and the derivation of dKH, although I wouldn't have been able to put all the bits together.

cheers Darrel


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## HiNtZ (15 Sep 2016)

This all good information for the archive.

Hopefully soon the google spiders will be along to get the thread in the search results. I think there's been a good discussion with lots of useful information.

Cheers guys. Loving this site more and more every day.


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