Combining methods of the ref KH solution with the pH meter

[Tom Barr]

Regarding Vaughn's and Gomer's ideas:

The good idea from all this is the fact it gets around the KH issue in the tank and variation it can cause.

We have folks claiming 50-200 ppm ranges of CO2 based on the pH/KH test readings and the fish are just fine, others have 35-50ppm and dead fish...........we know there's screwy issues with our assumptions about KH.

By using a referenced solution for the KH, we eliminate one variable/assumpotion that has been causing issues for sometime, but by using a pH color change to measure, we lose some of the accuracy.

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So this **obviously** leads us to make a referenced KH solution, that we can __insert a pH probe into__ so we can get very accurate deterimination of CO2 ppms.

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That way we have successfully removed the KH interference issues from the tank water and still have saved the accuracy of the pH meter.

You simply add the pH meter inside the solution of the drop checker.

Now that is **my idea** and one that would work very very well indeed. **Of course Gomer and Vaughn** also get credit for Ref KH solution (haha), but I've always just used the tank itself and done a huge water change with RO water or known tap to set the CO2.

Much like making a ref solution when you use EI and getting out of testing the water for NO3 etc.

Which is a similar thing...........but this way anyone without RO or having an unknown KH influence/interferences could get around this and both the pH and the Kh are referenced, unlike the old method of merely assuming the KH is all bicarbonate.

A similar set up is used but uses an IR for Limnology for the gas rather than a reagent based liquid etc.

So a small vial with the ref KH solution is added with an air gap to keep it seperate from the tank water, the solution has a pH probe with a rubber gasket inserted into it, that reading is referenced to the pH/KH table.

Basically you make a large probe holder with an air gap and a KH ref solution inside.

That should be cheap and solve both issues.

If you don't wanna fork out the $ for a meter and are fine with color metric test for pH, then this is a great idea also.

Either way, you come out ahead and have a mucher higher confidence and accuracy in your assumptions for the CO2 ppms at any point during the day being that both are continuous measurements.

That will be cool for many who are frustrated with measuring CO2.

Now with that extra acrylic I sitting and the viewtainers, and those nice rubber grommets, I can make a nice little KH ref chamber for the pH probe

Then you can measure CO2 in tannins laden water, ADA soil, funky tap, most anything.

Greg will not sell such solutions, liquids are harder to ship.
Someone would be wise to offer a series of KH ref solutions in 500ml amounts to 1ppm or less resolution using a 0.001 gram of lower scale using DI water.
Say 0-1-2-3-4-5-10-20 degree ranges.

So there you have it, another excellent way to measure CO2 very accurately and gets around intereferences from the tank's water.

Gievn the importantce of CO2 measure in our tanks and it's relation to algae and plant growth, I think folks should be very critical about CO2, I nag folks a lot about this

But......even this pH meter and ref solution will not address the intereference a CO2 microbubble might have.

Unlike the O2, Ar, N2 gases, these are non acidic and a will not affect the pH readings, one could make a deterimination as to the relative % change based on the CO2 mist method floating around the water vs and standard reference.

No other gases will affect the color or the pH in the ref solution.

This, in a sense, would allow you measure the true plant CO2 availability of the mist/dissolved fractions together.

The other more obvious way is to measure the differences in O2 production.

I've already done that and found roughly 20-40% increase in O2 production using a calibrated YSI DO meter.

Still, it's interesting to try out another method to measure CO2 with/without to see if the affect is close to the % increase in plant production.

I had my lawyer notorize the idea just a few minutes ago.
The aquaschisters are quick to snag anyone's ideas and call them their own, make $$ off of them, this way I can go after them legally and prevent some of that from happening. G abnd V will get 1/3 but I doubt folks will make any from this idea

I just do not want "thieves" to make $$ off of it and really just wanna help folks do better with aquatic plants.


Regards,
Tom Barr

 

[Tom Barr]

The patent thing, that's a joke FYI, seems some have gotten a bit worried about that

I might just to get back at some folks that do take things and do not give credit where it is due.

Regards,
Tom Barr

 

[yme]

I am sorry, I don't get it...

what is the KH reference solution? Is it a fluid with a known KH? or an indicator reagent that tells you the KH?
and what about the air gap and pH meter?

you put the pH meter in the KH reference solution? But will the KH reference solution not have a pH which is totally independent of the tank's pH?

And so and so on... basically I don't get it...

maybe a picture/drawing will make much clear?

greetz,

yme

 

[Tom Barr]

The KH reference solution you make yourself.
You use DI water and baking soda to make it very precise.

You place this solution in an air gapped container, this allows the gases to mix, but not KH, KH has no atmospheric component(at these temps anyway), whereas CO2 does.

So the CO2 can mix, but not the screwy tank water with it's tannins/non bicarb alkalinity and semi accurate KH test methods.

The pH probe adds more ACCURACY than the colormetric drop checker method and for those without good color preception eyc.

You also do not need a colormetric solution in the drop checker if you use a pH probe, just a ref KH water solution.

With a good pH probe and good accurate reference solution, you should be able to get very close.

The rate of response will be slower since the gas has to go to the the air gap and back into solution again.

But that's not too long I'd imagine.

Regards,
Tom Barr

 

[VaughnH]

YME, this technique relies upon the fact that if you seal the air above the water, so it doesn't leak to the atmosphere, the air above the water and the water will reach an equillibrium where both have whatever ppm of CO2 gives an equal absorption of CO2 back into the water and release of CO2 into that air. Now, if you connect a different container of water to that same air above the water, that container's water will also reach an equillibrium with the air, again so the CO2 escaping that water into the air and the CO2 being absorbed from that water by the air will be in equillibrium. The two bodies of water will end up with the same ppm of CO2 in them.

So, we use a bit of water, with a known KH, preferably 4 degrees in a little container which has an air "horn" that allows you to put the container under the tank's water surface, with air trapped in the "horn". The water in the little container will then soon have the same ppm of CO2 as the tank water. We have a pH indicator solution, the same one used for a pH test kit, in the bit of water in the little container, so the color of that water tells us what its pH is. When the KH of the bit of water is 4 degrees, the pH will be 6.6 when the water has 30 ppm of CO2 in it, and that pH 6.6 makes the indicator be green. If the CO2 ppm is low the color will be blue green, and if it is high the color will be yellow green.

We have now bypassed the effect of all of the sources of acidity or alkalinity in the tank water, because all we are testing from that water is the ppm of CO2.

I have just finished increasing the KH of the water in my little "drop checker" to 5.0, which will give a green color for pH=6.6, again, but that will now mean about 40 ppm of CO2 in the water. I'm doing this to see if the fish react badly to 40 ppm of CO2. I suspect that they don't.

 

[VaughnH]

The KH reference solution you make yourself.
You use DI water and baking soda to make it very precise.

You place this solution in an air gapped container, this allows the gases to mix, but not KH, KH has no atmospheric component(at these temps anyway), whereas CO2 does.

So the CO2 can mix, but not the screwy tank water with it's tannins/non bicarb alkalinity and semi accurate KH test methods.

The pH probe adds more ACCURACY than the colormetric drop checker method and for those without good color preception eyc.

You also do not need a colormetric solution in the drop checker if you use a pH probe, just a ref KH water solution.

With a good pH probe and good accurate reference solution, you should be able to get very close.

The rate of response will be slower since the gas has to go to the the air gap and back into solution again.

But that's not too long I'd imagine.

Regards,
Tom Barr

I found the "time constant" for this device is around 2-3 hours. And, that is fine because the CO2 concentration shouldn't be changing a whole lot faster than that anyway.

If you use standard probe calibration solutions of pH=7.01, the most accurate reference solution for measuring that the CO2 is at 30 ppm is one that gives a ph of 7 at 30 ppm, or KH=10.

 

[yme]

thanks!
I get the principle and I must say it is very smart thinking!!!!!

However, I have some practical issues concerning the design.
The principle is based on the assumption that the [CO2] of the KH reference solution, the air gap and the tank water is the same.
I think the most important question is: is this true???
I mean, the KH reference solution and the air gap are not in motion, so the diffusion will be slowed down. Does CO2 diffuse that easily into the airgap and subsequently into the KH reference solution or could there be a gradient? So could the [CO2] in the airgap be slightly lower than in the tank and could than the [CO2] in the KH reference solution be even lower?
If you enlarge the problem: if you have a "horn" of 1 meter, will the [CO2] in the KH reference solution be the same as in the tank? Will it just take some time to reach the equilibrium or will it never?

Of course it is easy to test:
take a tank, fill it with RO water and add the desired amount of carbonates. take a bit of the tank water as reference solution and put it in the horn of the "device". Connect the (pH controlled) CO2 equipment and aim p.e. for a [CO2] of 30 mg/l by setting the pH at the right value. Put now the "horn" in the tank and connect a second pH electrode to the horn. measure than the amount of time that it takes for the horn to equilibrate, or IF it equilibrates at all. Of course both pH electrodes must give accurate values.

Perhaps you did similar experiments?

greets,

yme

 

[VaughnH]

No, I didn't run that type of experiment, having been told many times over the years by many people that in a two container system with a sealed air gap, the CO2 will reach the same ppm in both water containers. It does take time for this to happen, my testing says that time is around 2-3 hours for the imitation ADA "drop checker".

 

[Tom Barr]

2-3 hours is a long time...............
The day is only 10 hours so you miss 2-3 hours on either end.

also, what is fine at 1-2 hours of the CO2 being on, is quite different 3-4 hours into the day cycle.

You are playing catch up the entire day.

The time constant can be reduced a number of ways though..........

1. Increase the surface area to Kh ref solution ratio. This would allow more gas to equilibrate faster based on Fick's 1st law.

2. Decrease the air gas distance, this based on Fick's 1st law will also increase the Flux

3. If you wanted to be very critical, temp can also be added into Fick's 1st law.

4. Reduced KH solution around probe, less volume of ref solution for the CO2 to diffuse evenly into.

5. There's more but I gotta run to a seminar

Regards,
Tom Barr

 

[VaughnH]

I got the 2-3 hours with the bulb of my device completely filled with KH reference water, leaving little surface area for the gas exchange. Now I have it only about 5/8 full, so the surface area is much greater and the volume of KH reference water is much smaller. I didn't check how fast it reached equillibrium today, and I was jacking up the bubble rate too, so I'm not sure I could have found a good number. Incidentally, all afternoon with 40 ppm (+/-5 ppm, probably) and no fish distress at all. I have 5 degrees KH water, and a very green color = 6.6 pH. After a week or so I may go on up to 6 degrees KH, but that one scares me a bit - a small error in judging green could give me 70 ppm of CO2, which I think will be far too much.