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Old 09/14/2017, 03:52 PM   #51
karimwassef
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I like the idea of measuring in-water CO2 as well as the air being injected.

It would help optimize my air injection. I'm currently running on maximum pressure ~30ft through two penductors with a massive vent fan to pressurize the external air through an 8" duct... overkill! But I know that I'm getting gallons of fresh air heavily aerating.


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Old 09/15/2017, 05:05 AM   #52
dartier
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I read the thread on the planted forum, both the one I found and the one that orcafood posted. They were by the same person. In both cases he was able to measure the amount of CO2 in his FW tank using the inexpensive IAQ CO2 sensor.

The 2 challenges he had was keeping the sensor dry, he was mounting it inside the housing with a silicone membrane and putting it below the water surface.

My suggestion would be to use the remote sensing cap that they offer and use an aqualifter pump to setup a closed loop through the sensing head. The pump offered from the vendor is quite pricey. For the sensing head, a 1/2" PVC tee, with the inline legs sealed with a 1/2" to 1/4" NPT adapter so that a John Guest fitting can be screwed in for each side of the loop.

For the 3rd leg of the tee, the membrane needs to seal this portion. I am still thinking about how to do this and make it maintainable. I am thinking a union that can be tightened on with the membrane trapped between the O-ring and the union face may be all that is needed. The breather bags were slow to pass the CO2 and reach equilibrium, but for our needs, that may be fine.

Lastly, they found the sensor was much quicker to update the lower below the water surface it was positioned. So for safety it would be nice to be able to detect a leak for water incursion and have the pump not pump it through the sensor. Still thinking about how to do this without impacting the internal air volume in a significant way.

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Old 09/15/2017, 05:18 AM   #53
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Quote:
Originally Posted by karimwassef View Post
I like the idea of measuring in-water CO2 as well as the air being injected.

It would help optimize my air injection. I'm currently running on maximum pressure ~30ft through two penductors with a massive vent fan to pressurize the external air through an 8" duct... overkill! But I know that I'm getting gallons of fresh air heavily aerating.
It would be very interesting to see how stable the levels of dissolved CO2 are in your setup


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Old 09/15/2017, 06:20 AM   #54
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I would compare the air CO2 to the water CO2 at different injection pressures over time...

The high pressure injection reduces the time for the air CO2 to impact the water CO2.

The water CO2 is not benign. It has its own forcing function as the tank actively consumes CO2... so the injection both adds and removes CO2 to keep the air and water tight.


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Old 09/15/2017, 03:01 PM   #55
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Is there any documentation on the type of silcone that he used? That's another interesting idea.


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Old 09/15/2017, 04:01 PM   #56
dartier
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Quote:
Originally Posted by bertoni View Post
Is there any documentation on the type of silcone that he used? That's another interesting idea.
I am not sure if this is the product he used, or he DIY'd one, but he did link this site as a possible supplier: http://www.sspinc.com/products/Thin-...4_category.htm

At one point he was talking about making his own between 2 pieces of saran wrap with a rolling pin, lol.

He mentions that the site above has 12" x 12" sheets that can be purchased.

Dennis


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Old 09/15/2017, 04:08 PM   #57
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The silicone diffusion rate would need to be factored in.

I'm interested in time ... so this is a big deal.


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Old 09/15/2017, 04:36 PM   #58
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That looks like an interesting approach. I agree that we'd need to know the velocity of carbon dioxide across the membrane. It'd be an interesting experiment if the cost is tolerable.


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Old 09/15/2017, 04:48 PM   #59
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I'm trying to gauge the rate of diffusion of air CO2 into aqueous CO2 and need to account for the rate of diffusion of CO2 through the membrane!

Don't like measuring time with a time error... but maybe it can be corrected for enough.


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Old 09/15/2017, 05:45 PM   #60
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I think a pipe sealed from the top in an overflow (low flow area) extended all the way to the bottom having no cap and some sort of inline fan like an aqualifter to keep the air moving through the top of the pipe to the sensor and back near the bottom so it is always full of air? Keep the sensor far from the water and bring air, which is under decent pressure from the top-capped bottom-open tube submerged. Then pack a bunch of desiccant into an inline filter before the sensor.


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Old 09/16/2017, 04:09 AM   #61
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What range do you think we should be planning to support? The vendor linked with the IAQ sensors offers a variety of ranges (and price points), with the most affordable supporting 0-10,000 ppm while ones that support 0-100,000 ppm are 3 x the price (and 1/3 as accurate 30 ppm | 100 ppm).

Is 10,000 ppm a reasonable limit to expect that may diffuse out of the water into the headspace of the sensing head?

Dennis


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Old 09/16/2017, 04:25 AM   #62
orcafood
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There is around 400 ppm in the air outside, closer to .5 ppm dissolves into the tank water as co2, a headspace should give a depressed readout compared with the outside co2, low range is best.


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Last edited by orcafood; 09/16/2017 at 04:38 AM.
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Old 09/16/2017, 06:33 AM   #63
karimwassef
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300-900 is what I've found meaningful for my reef


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