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Old 11-04-2012, 09:33 PM   #16
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As always, the biggest problem with trying to measure the concentration of CO2 in a planted tank is that it varies a lot from spot to spot in the tank. Near fast growing plants it will be low, compared to near the input of CO2 enriched water. Near the surface it will be less than in the middle of the tank. I once saw this demonstrated, when Plantbrain first played around with his $2000+ CO2 probe.

If this device can measure the concentration of CO2 in the air in a .03 thick sheet of air on top of the water, it should not take more than seconds to reach an equilibrium with that in the water, just below the surface. But, if that volume of air is a cube 6 inches on a side, it will take a lot longer. Or, if it is a large volume with a small interface with the water it will take even longer.

I still like the idea - and Murphy's Law, like Einstein's Relativity Theory, has yet to be found incorrect (Henry and I aren't acquainted.)
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Old 11-04-2012, 11:52 PM   #17
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I'll stuff it in a breather bag to test things out. I'll think about the design of the enclosure later.

Here's a link on how to interface it with the arduino
http://www.co2meters.com/Documentati...duino-uart.pdf

I'll have to make a bunch of Close enough par sensors first before I get to this.
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Old 11-05-2012, 11:52 AM   #18
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This looks like it has potential.
Worthy of more r&d.
Keep the inovation flowing mg
mD
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Old 11-07-2012, 07:24 PM   #19
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The sensor arrived.

Cost: $75 shipped

Will have to get some breather bags.
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Old 11-07-2012, 07:42 PM   #20
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I think you'd need close to 2000 ppm or so in the head space to get 25-30ppm in solution. I did the calculation back in 1998 for a class for CO2 rise and the impacts in freshwater. This assumes that the 2 systems are in equilibrium, but that is rarely the case.

The issue is that the sensor will be slow, just like those Drop checkers.
A pH meter and relative change in degassed vs enriched would work much better and be more responsive.

In other words, a 90-100 pH meter would likely fit the bill much better.

Worth a shot though.

Since lag time is a factor, a pH/CO2 standard could be done using this at different times through the day for checking the pH meter vs the pH/KH/CO2 chart. But the lag time and stability of the system need accounted for.
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Old 11-07-2012, 07:55 PM   #21
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Thanks for the input.

Is a pH meter practical? You'd have to constantly calibrate your readings.
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Old 11-07-2012, 08:26 PM   #22
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Quote:
Originally Posted by mistergreen View Post
Thanks for the input.

Is a pH meter practical? You'd have to constantly calibrate your readings.
pH meter is, we have successfully used them quite well in the hobby for nearly 25 years.

For the $, I think you'd be better off with a good pH meter. You calibrate the probe maybe 1x a month or if you want to be very certain. Good general care for the tip etc.
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Old 11-08-2012, 06:44 AM   #23
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If the sensor life expectancy lasts even half of the predicted >15 years quoted on the supplier site that could be an interesting pro for the new CO2 sensor vs pH probe systems as well.

Assuming 1 year life span on double junction probes. (8 -14 months has been my personal experience) @ 35 bucks a probe. This obviously adds up.

And please tell me if I should be using better probes. that give me better longevity. Ive been going with the Milwaukee's and been happy with them since I usually get a year out of them with monthly calibration and gentle cleaning.

Tom, while I understand what you are saying about lag time and the sensor not being all that responsive, i think there is still one major advantage here.

While the pH meter obviously has served us well and can tell us the maximum amount of CO2 that could be dissolved in our water for a given KH. This could finally help the hobbyist with more money than sense, that won't listen to me that the number on the chart is a maximum and continues to insist that his pH/KH chart tells him that he has 100ppm CO2 so his lackluster plant growth could not possibly be from lack of CO2

But seriously Mistergreen I am excited about this. As a group I don't think aquarists accept change well. Its nice to see someone pushing the limits with new tech.
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Old 11-08-2012, 03:10 PM   #24
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Hey MisterGreen- This sounds like another really cool project. If the science involved can be sorted out and a fairly accurate prototype built, maybe we can build a "Close enough Ph Controller" too.
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Old 11-08-2012, 03:24 PM   #25
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Yeah, hopefully with this gizmo we can eliminate over gassing your fish and BBA.

In terms of response time, it should be a good as the $2000 CO2 sensor but not as accurate obviously
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Old 11-10-2012, 09:41 PM   #26
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I had a chance to play with it. It's reading ambient air with ~2000ppm of CO2 and as soon as I dunk it in water inside a breather bag it shot up to ~8000ppm - 10,000pmm (maxed out)... I contacted the manufacturer to see what's up. I though air was only suppose to have ~360ppm and CO2 in water is suppose to be less than air.
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Old 11-11-2012, 02:55 AM   #27
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How can a sensor like this ever be calibrated?
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Old 11-11-2012, 03:05 AM   #28
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There's a manual on calibration. I read briefly that it needed to warm up a little. I left it alone for 10 minute and it went down to ~800 ppm. The sensor was around a fan. I wonder if air movement or water movement shoots up the readings.
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Old 11-11-2012, 02:42 PM   #29
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Oh interesting. CO2 level is high in the room. I stuck it out the window and it went down to 400-500. That seems right. Time to dunk it in water again.
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Old 11-11-2012, 05:05 PM   #30
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Does this work by shining a beam of IR light through a length of air gap, and measuring the absorption in the wave length band that CO2 absorbs? If so, it must require a flow of air through the air gap. And, if that's the case there would be a minimum volume of air around the sensor that would be needed to refresh the air in the gap so it can follow the fluctuations in CO2 content. Or, am I off on a tangent here?
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