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

[mordalphus]

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.

[jcgd]

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.

[plantbrain]

Originally Posted by Hoppy

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:

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


At least you try

[Bettatail]

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

[Jeffww]

Originally Posted by jcgd

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.

[galabar]

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

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[galabar]

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.

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[Jeffww]

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.

[mordalphus]

Originally Posted by Jeffww

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.

[galabar]

Originally Posted by mordalphus

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 ).

[galabar]

Originally Posted by MiamiArt

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.

[Hoppy]

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.

[galabar]

Originally Posted by Hoppy

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?

[Hoppy]

Originally Posted by galabar

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.

[samamorgan]

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.