# Converting a pH meter to a CO2 meter for more accurate CO2 control



## SMinNC (Mar 28, 2012)

How about a Breather Bag for shipping fish?

*Disclaimer:
I've never used one(breather bag). Still new to plants and only DIY CO2 so far. Never had a probe of any type.


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## Jeffww (Aug 6, 2010)

I never knew parafilm was permeable I just thought it was wax lol. Interesting...I'm not sure if it would provide a good rate of exchange though. It might end up just taking several hours to react so it wouldn't be a good meter. 

If we're really wanting to know how much CO2 is in our water we might as well just buy a CO2 probe.

You just need a laptop with a logging program or even a TI calculator with the appropriate installations...the 600 dollar probe...and you're set to go.


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## MiamiArt (Aug 27, 2010)

The thinking is to try to come up with something anyone can do.


Regards,

Art


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## Hoppy (Dec 24, 2005)

That film is a good find. If I had that a few years ago when I was trying to make drop checkers with a film in place of an air gap I would have been delighted.

It would be very easy to enclose a pH probe end with this film, but getting the standard KH water enclosed inside is much more difficult. I would probably try it by making an assembly tool that would hold the film shaped into a pocket, then fill the pocket with the water, stick the probe into the water filled pocket and mold the film around the end of the probe with the water trapped inside. Easy in principle, but probably very tricky to actually do it. The less of the water you trap, the shorter the reaction time for CO2 measurement.

I no longer have a CO2 system or a workshop, and don't have a pH meter or probe, or I would be tempted.


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## MiamiArt (Aug 27, 2010)

Hoppy,

I was thinking just a piece of acrylic tubing with one end capped. The capped end would have holes drilled into it and the film would lie on it somehow. The KH solution would be in this tube with the probe placed into it.

Like you said, easy in principal but harder to actually make...


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## Hoppy (Dec 24, 2005)

This probe is shaped about right, and the diameter is small: http://www.google.com/products/cata...=X&ei=qoB3T6eoMdPPiAL08O2nDg&ved=0CIUBEPMCMAM

It has a sensor diameter of 5/16 inch, so you could drill a slightly larger hole in a piece of wood, maybe 1/4 inch deep. Take a square of the film and a piece of 5/16 wood dowel, and poke the film into the hole leaving a 1/4 inch deep pocket for the water. Fill the recess with the water, and stick the probe in on top of the water and push it down as far as possible. Form the film around the probe and put a rubber band or O-ring over it to be sure it stays there. The result might be a standard KH filled probe end, so when you stuck it into the aquarium it would be a pH sensor/drop checker. Now, I just have to find a factory to make a few thousand of these before the world beats a path to my door:biggrin: (And, I need to get my money before any problems show up, like the probe taking 10 hours to stabilize, or the KH water oozing out, etc.)


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## jcgd (Feb 18, 2004)

What about a Heyco liquid tight cord connector, threaded into a coupling with the film somehow attached/ glued over the end. This is all I have lying around, but you get the idea. You would only have to unscrew the coupling and screw on a new one to change out the film.


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## jcgd (Feb 18, 2004)

Okay, apparently the film is self sealing. I assume it's like a sticker? That would make it easy to stick it to a coupling. I someone knows where I can get these films I could try it. I have a spare ph controller, and, well, everything else that I anyone could think of.


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## Hoppy (Dec 24, 2005)

That particular site only sells big lots of the film. Enough for thousands of probes. Googling didn't help a lot either, $20 for one roll was the cheapest I saw, but at least there are several places to buy it. Maybe it is possible to get a free sample?


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## jcgd (Feb 18, 2004)

Checked for it on the Bay of E.

I found a 2"x10 foot roll for about $7 shipped. I bought one. I'll update when if finally makes it to Canada and send out some samples if people like.


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## Hoppy (Dec 24, 2005)

jcgd said:


> Checked for it on the Bay of E.
> 
> I found a 2"x10 foot roll for about $7 shipped. I bought one. I'll update when if finally makes it to Canada and send out some samples if people like.


That's great news! I never once thought of checking that place. What does your pH probe look like? Maybe there is a really easy way to use the membrane to trap water around the sensing part - like assembling it with your hands and the probe under water.


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## plantbrain (Dec 15, 2003)

There are silicone films that have a better transfer rate of gas.

A flat tip pH probe also would be easier to add a cap to and refill with a known reference KH solution.

Now.........once all this is said and done..........how do plan to check to see the response times and the accuracy against a known standard?

Here's how:

You need a 500ml full bottle/jar, flask with a grommet, sealed 1/2" for the pH probe to added with the film membrane and cap so it does not tear.

Try and get all the air gap out with some DI water.
Measure the DI water, or better yet, bubble N2 gas to remove all the other gases like O2 and CO2.

Now buy some dry ice at the local grocery store, cut and weight a small amount of it, say 25 mg and add this very fast to the flask and cap.

25mg in 500mls = 50ppm of CO2 once it melts.

Next, you can do the same thing for 10ppm, and 100ppm etc.


If you use a larger volume of water, and dry ice, the accuracy should increase. N2 gas is likely available from a few different outlets.
Or you can measure the DI+ sodium carbonate with a pH probe and get a certain ppm etc.

This should be pretty accurate. I did this a few times recently.

I suppose the fish breather bags should work also, might be a bit fragile.
They have a a very large surface area relative the gas exchange rate for fish vs a small tiny pH probe tip. The trade off is the volume in the tip of the pH needs to be small and the KH solution layer needs to be thin.
This increases the response time considerably.

I spoke awhile ago to American Marine about making one for their pH probes, but they dropped the ball. A good idea and a way to make extra $.........down the tubes, I guess they make enough money?? :icon_roll

Rather than DIY, it would be nice for a vendor to make and carry one.


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## Hoppy (Dec 24, 2005)

plantbrain said:


> There are silicone films that have a better transfer rate of gas.


Have you done any testing with the Parafilm M as a membrane? It is hard to relate the CO2 diffusion rate they claim to a response time for the way we would use it.

For the accuracy part: If it would just measure the pH accurately, say to +/-0.1 pH, we should be able to make a KH solution with very good accuracy, so that would still be a much more accurate CO2 measurement than a drop checker gives us, where judging the color is so hard. For an absolute calibration vs a known ppm of CO2, that seems like a losing proposition all the way. We could certainly make a solution using dry ice, but getting it to be accurate sure looks questionable.


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## Hoppy (Dec 24, 2005)

From the website for Parafilm M:
"Permeability Characteristics:

Carbon Dioxide (Modulated IR Method): 1200 cc/m2 d at 23°C and 0% RH"

Does this mean 1200 cc/m2 per day? If so, this isn't likely to work. I did some calculating and for a .5 inch diameter probe, with a .5 inch diameter by .5 inch volume of standard dKH water enclosing the probe, it would diffuse about 8 ppm of CO2 per hour through the film. That wouldn't work for fast response, assuming I didn't make mistakes.


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## mordalphus (Jun 23, 2010)

You can always use what professionals use to measure gas exchange, which is LDPE. Any LDPE bag (lower the mil thickness, the faster gas is exchanged) will allow gasses to pass through, but hold liquid. Low density polyethylene is what breather bags are made from, as well as "breathing" membranes for mining and geological survey to measure gasses which are present in the earth.


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## jcgd (Feb 18, 2004)

Any idea what particular kind of bag would be best suited, Mordalphus? I thought in another thread the breather bag idea was shot down or disproved.


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## plantbrain (Dec 15, 2003)

Hoppy said:


> For the accuracy part: If it would just measure the pH accurately, say to +/-0.1 pH, we should be able to make a KH solution with very good accuracy, so that would still be a much more accurate CO2 measurement than a drop checker gives us, where judging the color is so hard. For an absolute calibration vs a known ppm of CO2, that seems like a losing proposition all the way. We could certainly make a solution using dry ice, but getting it to be accurate sure looks questionable.


This is the big issue with the drop checker.......but not only that....the Drop checker has a limited range it can measure unless you set up several over a wider range, that's a PITA, we also assume we need a certain ppm of CO2, this is also a big issue/problem.

Any particularly tank will have a very wide range where the target CO2 ppm is very different.

Dry ice works well if you are quick about it and have a sealable flask and probe holder.

Some guy suggested and claimed(I have serious doubts having tried it once.......) to use 12 gram CO2 paintball cartridges dissolved in water. Sounds good, till.........I tried to unleash the gas into water and a sealed container without breaking the glassware from the pressure. I think the guy was just being argumentative/wanting win the debate/save face and had never done it himself:icon_idea:

When you try different methods, you quickly learn the issues with various testing and experimental set up.


At least you try:thumbsup:


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## Bettatail (Feb 12, 2009)

Is the membranes stop exchanging K+ Monatomic ion? and only allow the co2 pass?


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## Jeffww (Aug 6, 2010)

jcgd said:


> Okay, apparently the film is self sealing. I assume it's like a sticker? That would make it easy to stick it to a coupling. I someone knows where I can get these films I could try it. I have a spare ph controller, and, well, everything else that I anyone could think of.



Parafilm is like thin sheets of wax. Imagine the stuff they put on cheese cut up into sheets. We use them in the lab to wrap and seal tubes for centrifuging and stuff. 

As for the breather bags...Again...I'm not 100% certain if the rxn will happen fast enough. Making a CO2 probe that only reacts 3 hours after any changes occurs isn't really a good detector...I have no experience with making a probe so I can't say how permeable breather bags are but I don't think they're more permeable than the interaction between air and water. Meaning you will never get faster than a drop checker's speed without making the fluid layer extremely thin. And so considering that a drop checker can take upwards an hour to react you're looking at a very slow rate.


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## galabar (Oct 19, 2011)

I might be missinh something. However, wouldn't a simple drop checker, using the same proposed method react just as quickly?

Sent from my HTC Glacier using Tapatalk


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## galabar (Oct 19, 2011)

Also, wouldn't contamination quickly clog the film? So far, it seems the best you can do is a drop checker that contains a Ph probe. You would get the same reaction time, but be a bit more accurate.

Sent from my HTC Glacier using Tapatalk


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## Jeffww (Aug 6, 2010)

Why hasn't anyone just used an O2 probe and crank up the CO2 until maximum O2 production is reached and if there is no limit without gassing their fish then we know your lighting is absolutely too high? I mean I suppose that O2 may never maximize since these plants were really adapted to grow on air and their efficiency is more a factor on light than anything else but it's just a thought...I'm trying to figure out why exactly you would need to know the precise concentration of CO2 or any gas really... 

edit: Actually I think O2 might reach saturation wayyyy before you find an optimal rate.


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## mordalphus (Jun 23, 2010)

Jeffww said:


> Parafilm is like thin sheets of wax. Imagine the stuff they put on cheese cut up into sheets. We use them in the lab to wrap and seal tubes for centrifuging and stuff.
> 
> As for the breather bags...Again...I'm not 100% certain if the rxn will happen fast enough. Making a CO2 probe that only reacts 3 hours after any changes occurs isn't really a good detector...I have no experience with making a probe so I can't say how permeable breather bags are but I don't think they're more permeable than the interaction between air and water. Meaning you will never get faster than a drop checker's speed without making the fluid layer extremely thin. And so considering that a drop checker can take upwards an hour to react you're looking at a very slow rate.


A drop checker's speed is slower because the co2 has to disperse into the air chamber of the drop checker, and then diffuse BACK into the fluid inside. With a membrane and no air space, the co2 would simply move through the membrane and not have to wait to diffuse back into the water. It would be much quicker I would think. And a breather bag allows co2 to pass through it pretty quickly. I think the mil thickness of breather bags is 2 mil, so if that was lowered to 1 mil or less, the breathing would be even faster. 1 mil LDPE bags are available almost everywhere. I'm pretty sure standard grocery produce bags (the thin annoying bag that is impossible to open when you're holding a bunch of lightly misted beets) are LDPE at less than 1 mil thickness.


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## galabar (Oct 19, 2011)

mordalphus said:


> A drop checker's speed is slower because the co2 has to disperse into the air chamber of the drop checker, and then diffuse BACK into the fluid inside. With a membrane and no air space, the co2 would simply move through the membrane and not have to wait to diffuse back into the water. It would be much quicker I would think. And a breather bag allows co2 to pass through it pretty quickly. I think the mil thickness of breather bags is 2 mil, so if that was lowered to 1 mil or less, the breathing would be even faster. 1 mil LDPE bags are available almost everywhere. I'm pretty sure standard grocery produce bags (the thin annoying bag that is impossible to open when you're holding a bunch of lightly misted beets) are LDPE at less than 1 mil thickness.


I think I am seeing a pattern here with this topic.

The topic is arguing for a better solution than a drop checker and says that the new solution is better in X, Y, and Z.

However, if the new solution can be applied to a standard drop checker, then you really can't say that the new solution is better in X, Y, and Z.

For example, if you simply had drop checker fluid sitting in the film media, you would get the same speed of change that you are talking about with the new solution.

However, again, with contamination issues and the fact that no one can say for sure that CO2 would move more quickly into solution through the film rather than through air, I don't see this as being an improvement (but I'll wait and see  ).


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## galabar (Oct 19, 2011)

MiamiArt said:


> Hi everyone,
> 
> In my humble opinion, I think that we need to get a better handle on one of the most important aspects to plant keeping- CO2. If you're adding it to the aquarium, you need to be able to control it.


I understand that this is an opinion. However, the opposite opinion seems reasonable -- that the ubiquitous drop checker is good enough. Folks seem to be able to grow plants extremely well with just a drop checker and it doesn't seem to be a pain point or source of concern for most.

At least I don't see many posts complaining that, but for a better measure of CO2, their poorly performing aquarium would do so much better.


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## Hoppy (Dec 24, 2005)

A few years ago I did some testing with membrane type drop checkers, using several types of membranes. As long as the amount of fluid in the DC is very small, and the area in contact with the membrane is very large, I was able to get reaction times less than 30 minutes. The primary cause for the fast reaction time, in my opinion, was the large ratio of surface area to volume of the fluid. But, the disadvantages were the difficulty in putting fluid in them, the extreme difficulty seeing the color of the fluid with such a thin layer, and the short lifetime of the DC per filling of fluid. By far the best membrane was one made for oxygen probes, as I recall, but it was also by far the hardest to work with due to its being so thin and so lacking in strength. Breather bag material barely worked at all. Material from a priority mail envelope worked fairly good. I stopped working on it when I ran out of good ideas to try.


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## galabar (Oct 19, 2011)

Hoppy said:


> A few years ago I did some testing with membrane type drop checkers, using several types of membranes. As long as the amount of fluid in the DC is very small, and the area in contact with the membrane is very large, I was able to get reaction times less than 30 minutes. The primary cause for the fast reaction time, in my opinion, was the large ratio of surface area to volume of the fluid. But, the disadvantages were the difficulty in putting fluid in them, the extreme difficulty seeing the color of the fluid with such a thin layer, and the short lifetime of the DC per filling of fluid. By far the best membrane was one made for oxygen probes, as I recall, but it was also by far the hardest to work with due to its being so thin and so lacking in strength. Breather bag material barely worked at all. Material from a priority mail envelope worked fairly good. I stopped working on it when I ran out of good ideas to try.


Was this (30 minutes) significantly faster than the fastest working standard (air/water) drop checkers? Also, did you try any longevity tests with the material?


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## Hoppy (Dec 24, 2005)

galabar said:


> Was this (30 minutes) significantly faster than the fastest working standard (air/water) drop checkers? Also, did you try any longevity tests with the material?


The fastest I have ever had a regular drop checker work was around one hour. And I have made and tested dozens of drop checkers of various designs. I never had one of the membrane drop checkers last more than a couple of days in my tank. The membrane didn't fail, but the tiny amount of fluid in them was easily diluted by even minute leaks. So, the color would vanish completely. It is a lot easier to keep one ml of fluid working than to keep .01 ml working. No membrane is perfect. The leak very little water through them, approaching zero, but not zero. So, with such a small amount of standard KH water, that tiny leakage ruins the KH water. It would be different if the KH water was in a spherical container, but when it is just a thin film it became impossible.


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## samamorgan (Dec 31, 2011)

I had the same idea galabar had when i saw this post come up. It does make sense that the transmission rate of Co2 would still be about the same. But there is one idea i don't see floating around yet. With a PH probe in a standard drop chcker setup, you would still get a much more exact Co2 reading than just a vague color. That would be a definite improvement over what we have going currently. I don't think fast response time is an essential component, but accruate readings would be very nice.


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## galabar (Oct 19, 2011)

samamorgan said:


> I had the same idea galabar had when i saw this post come up. It does make sense that the transmission rate of Co2 would still be about the same. But there is one idea i don't see floating around yet. With a PH probe in a standard drop chcker setup, you would still get a much more exact Co2 reading than just a vague color. That would be a definite improvement over what we have going currently. I don't think fast response time is an essential component, but accruate readings would be very nice.


That was one of the thoughts that popped into my head too.  It wouldn't be too hard for a manufacturer to create a little fitting for the end of a Ph probe that contained a small amount of reference solution and an air/water interface.


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## jcgd (Feb 18, 2004)

samamorgan said:


> It does make sense that the transmission rate of Co2 would still be about the same.


I don't understand this. Why would it be about the same? Gas in liquid to air to liquid would have a completely different transmission rate than gas in liquid to gas in liquid.

Another simple solution is two different checkers with solutions of different kH that are both green at a certain ppm. They will be different shades, but if you do it right, both will be green at a certain ppm. You can get pretty close, within about 5ppm with this method rather than the +/- 15ppm with a single checker.


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## jcgd (Feb 18, 2004)

galabar said:


> I understand that this is an opinion. However, the opposite opinion seems reasonable -- that the ubiquitous drop checker is good enough. Folks seem to be able to grow plants extremely well with just a drop checker and it doesn't seem to be a pain point or source of concern for most.
> 
> At least I don't see many posts complaining that, but for a better measure of CO2, their poorly performing aquarium would do so much better.


I can pour water in a bucket, stick it outside and have java fern grow just fine for weeks. I had moss in a sealed bag with some water for a full year and it lived and grew. This doesn't do anything to scratch my itch for the hobby.

Just because stuff is working fine doesn't mean we can't improve. You can also have fine co2 levels and have other issues creating a poorly performing aquarium. If we can be exact with co2, it's one more thing crossed off the list.


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## samamorgan (Dec 31, 2011)

I wasn't talking about membrane transmission. Read the entire post.


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## MiamiArt (Aug 27, 2010)

So, I was enjoying the back and forth. It's a good debate.

Did we conclude it's a theoretical possibility worthy of someone attempting it?

Thanks!


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## mordalphus (Jun 23, 2010)

I have a breathing bag and a tank with co2, would be as easy as putting some ph indicator and 4dkh in it and sinking it to see how fast it works? I'll try tonight


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## jcgd (Feb 18, 2004)

I'm waiting on the tape to arrive from bay of E. Should be here in a few days. I don't think it's gonna go anywhere, but the stuff is supposed to be good for a bunch of uses.


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## mordalphus (Jun 23, 2010)

Breather bag worked for me, I put 5ml of 4dkh in a breather bag put in 5 drops of pH indicator, and within 30 minutes it had changed. I might have just invented the worlds cheapest and easiest drop checker!

I don't know if 30 minutes to change the pH from blue to light green is fast enough, but maybe with less fluid it would be faster?

Worth trying out anyways

EDIT:

Here's pics. They're the same color in real life, but the drop checker is so close to the light that it washed out.

Anyway, this is after 25 minutes:


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## Hoppy (Dec 24, 2005)

Very good! Now you need to figure out an effective way to hold the drop checker in position, preferably with a white background.


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## Jeffww (Aug 6, 2010)

Very interesting. I'll follow this closely.


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## mordalphus (Jun 23, 2010)

A little update on breather bags. They disperse and absorb co2 much faster under water than they do out of water. Last night after I was done with my little experiment, I took it out of the water and placed it on my hood, and it took a long time out of water to get the co2 out of the bag. Under water it took much less time. 

I don't see why you couldn't just rubberband a breather bag with some 4dkh in it over your probe and use it like that?


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## Hoppy (Dec 24, 2005)

mordalphus said:


> I don't see why you couldn't just rubberband a breather bag with some 4dkh in it over your probe and use it like that?


One reason you got a fast reaction was the large surface area of the bag, compared to the fluid volume. If you were to enclose a pH probe with a breather bag it would need to be in a way that also gives you a large surface area compared to the fluid volume. For the cheaper probes this is probably easy to do, but for flat face, more expensive probes it would be more difficult. One advantage of this is that the 4 dKH water could also be the storage fluid for the probe between uses? (I think)


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## mordalphus (Jun 23, 2010)

Oh definitely it could be storage liquid.

However, I think putting this on a standard pH probe (you know, milwaukee or hanna), would yield just as much if not more surface area for the bag. You know, it would look like a ball of liquid at the tip... I suppose I should just shut up and try it out.


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## mordalphus (Jun 23, 2010)

Ok, so I did it, and spot on, my pH levelled out in 15 minutes.

Here's the jerryrigged probe:









By the time I went to grab my camera, the pH had gone from 8.0 to 7.9:









15 minutes later, it was bouncing between 6.5 and 6.6, where it is now:









So in theory, I have a 1.5 degree drop in pH making my co2 in the tank what? As reference, my drop checker is a greenish-yellow (heavy on the yellow). This is generally where I keep my co2, my fish shrimp and cpo seem fine, but if I turn the co2 up more, they start to croak.


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## mordalphus (Jun 23, 2010)

I've turned my CO2 off, and have lifted the filter output above the water level to outgas and see how long it takes for the co2 to dissipate out of the breather bag now.

It wont work very well if the co2 can enter the bag but then not leave it at the same pace.


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## Rockhoe14er (Jan 19, 2011)

I had this same idea. I am going to try this too.


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## Hoppy (Dec 24, 2005)

A pH of 6.6 and KH of 4 degrees is 30 ppm of CO2. Congratulations, you just made a fast reaction, inexpensive CO2 probe. I don't think the rise in pH in air is a good test. Instead, get a glass of tap water and stick it in there. That is where the probe has to react to a drop in CO2 ppm, in water, not in air.


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## jcgd (Feb 18, 2004)

mordalphus said:


> I've turned my CO2 off, and have lifted the filter output above the water level to outgas and see how long it takes for the co2 to dissipate out of the breather bag now.
> 
> It wont work very well if the co2 can enter the bag but then not leave it at the same pace.





Hoppy said:


> A pH of 6.6 and KH of 4 degrees is 30 ppm of CO2. Congratulations, you just made a fast reaction, inexpensive CO2 probe. I don't think the rise in pH in air is a good test. Instead, get a glass of tap water and stick it in there. That is where the probe has to react to a drop in CO2 ppm, in water, not in air.


I bet you if you put it in the jar it would equalize the other way at the same pace. I doubt the bag membrane is directional as far a gas exchange goes, but instead it is something different about the mechanics of a gas diffusing from water to water (even with the membrane) then the mechanics of it diffusing from water to air. 

My girlfriend did a study on solute transport through non living membranes so I'll read it and report back on my findings.

The thing I love about this method is that the natural ph swings of a tank (over days or weeks) have no effect on the ph reading and as a result, gas delivery if you are using a controller. Solved my last anxiety about precise co2 delivery... so precise that co2 consideration is set and forget. It is one more thing to add to the non-issue list of keeping a planted tank. Co2 using a method like the one be tried takes away any worry of not having enough co2 when looking to solve other issues.

Mordalphus, can you try timing the change of the ph with the probe in the membrane both ways, as in time to turn green, time to go back when the co2 is off and being gasses away?


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## mordalphus (Jun 23, 2010)

So I went out for dinner and came back, with no change in the pH, so I took my probe out of the bag and tested the tank water, and there was almost no co2 left. (normally my pH is 7.3 in my tank with no co2, and I turn my pH controller to 6.5) The pH was 7.1. So obviously something is haywire about the transfer back out of the bag.

I'm not sure why this is, doesn't seem like there should be a reason for the pH inside of the bag to go down, but then not go back up, unless it's not just gas that's passing through the bag, and maybe some errant ions are making their way through as well?


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## Jeffww (Aug 6, 2010)

There's a ton of CO2 in the air too. It probably equilibrated at that level.


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## Rockhoe14er (Jan 19, 2011)

Jeffww said:


> There's a ton of CO2 in the air too. It probably equilibrated at that level.


Actually the co2 in the air is very very small. The air that we breath in our lungs has 0% co2, 21% oxygen and 79% Nitrogen. I think co2 in the air is much smaller than we think it is. It's still much easier for plants to get co2 because of the speed that gasses disperse in air vs about 10,000x slower in water. 

I think it sounds like something else might be going through the membrane or some of the bicarb in the KH mixture could have been converted to co2 and water and left the solution. Even though it's a slow reaction without enzymes it's still possible for bicarb to be converted to co2 and water. This could dilute your 4dkh solution and make the water softer which could explain the lower pH reading. I would test your kH mixture and see if you are still getting 4 degrees.


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## Hoppy (Dec 24, 2005)

jcgd said:


> The thing I love about this method is that the natural ph swings of a tank (over days or weeks) have no effect on the ph reading and as a result, gas delivery if you are using a controller. Solved my last anxiety about precise co2 delivery... so precise that co2 consideration is set and forget. It is one more thing to add to the non-issue list of keeping a planted tank. Co2 using a method like the one be tried takes away any worry of not having enough co2 when looking to solve other issues.


This doesn't quite solve the CO2 measuring problem. The remaining part of the problem is the wide variation in concentration of CO2 at different places in the tank, at least with high light. If you pick a good enough spot in the tank, and the plant mass distribution doesn't change much, this could be a very good way to use a pH controller. But, once the plant mass distribution in the tank changes much, the good enough spot may not be typical of the actual average CO2 concentration. In any case this would be a great improvement over the normal use of a pH controller. (If you can resolve the problem of slow rise of pH as the tank concentration goes down.)

I think I would try to reduce the volume of water trapped in the breather bag, and also test how long the "charge" of KH water continues to work right. Also, the breather bag may not be the best material for the membrane. Some other materials need to be tested.


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## m8e (Oct 16, 2009)

Hoppy said:


> I think I would try to reduce the volume of water trapped in the breather bag, and also test how long the "charge" of KH water continues to work right. Also, the breather bag may not be the best material for the membrane. Some other materials need to be tested.


I think it's the surface area to volume ratio that important here. i.e the bag should be as flat as possible.


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## mordalphus (Jun 23, 2010)

I was reading on kordon breather bags, and they say that co2 is able to pass through the liner at more than twice the rate of other gasses. Could this be the problem? That the co2 gets trapped into the bag, and there's nothing else that is pushing it out? I really dont understand why the pH didn't go back up, especially when it went down so quickly.


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