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CO2 analog sensor
Hi Rob, happy new year!

I picked up a standalone wall-mounted CO2 sensor while trying to diagnose a consistently low pH problem. ( ) It has outputs of 0-5V, 0-10V, or 4-20mA, all corresponding to 0-2000ppm CO2. Is there a way to tie in an analog sensor like this to the controller? I'm currently just using a multimeter to read the value, but it would be nice to at least have a real display and/or some kind of data-logging for it.


p.s. about $60 on ebay if anyone is looking for one
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Hi Skwerl77, thanks happy new year to you as well.

That's a nice looking sensor, it should work on an analog port when set to 0-5v. Of course there's no code to map out the 2000ppm but you could still use it with the custom rules if you pull out a calculator for now. Later down the road I do plan to add some mapping for co2.

The analog pins reads 0-5v and translates that into a number from 0-1023, 1023 being 5v. In the custom rules for analog sensors you can select a value in this range. If you wanted to have something happen when the sensor read 1000ppm you would set the rule value to 511. If you want to trigger at 500ppm set the rule value to 255.
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HI I guess I am still a little confused as how that reads CO2 in the water a general wall mount reading room present co2 is not going to be the same as what is dissolved in the water. also if your tank is a planted fresh water tank and is having very low Ph one thing to try is stirring up the bottom I hade a similar problem a while back and it was all caused by dead spots under some large drift wood pieces I had the break down reaction was generating a weak acid and over time it beat out the waters ability to buffer I was killing myself to figure it out and the local fish stores where no help really they just wanted me to keep buying buffers. Hope this might help I had to tear down half my tank to fix it 180G tank no fun doing that
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Hi Rott, my thought was he had no plans to read a tanks CO2 but I didn't really notice the low ph issue. But yeah good point this won't help with an aquarium. Some people use the controller for horticulture so that's what I was thinking.
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It's not so much a measurement of the CO2 in the water, but pH is almost directly affected by the ambient CO2 levels in the air surrounding the tank because dissolved CO2 becomes carbonic acid which lowers the pH. Normal seawater out in the ocean is exposed to a pretty stable 350ppm CO2, but in a house the CO2 levels can be greater than 1000ppm, thus increasing the amount of carbonic acid higher than normal seawater. I actually run a CO2 scrubber attached to the air inlet of my skimmer, basically a filter housing filled with soda lime that absorbs CO2, but it isn't helping much. I wanted to see how bad the air was in my house, and just using the multimeter reading of about 5 volts, I think I'm seeing about 1000ppm in the house. Not really sure where to go from here, I already dose kalkwasser, maybe a house ventilation system. From what I've read, opening windows seems to help. Just not in New England in January! Don't really plan on controlling anything with it, just trying to confirm what's going on in the house.

Pretty good write up here if you're really interested:
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Who would have known, always learning something. One day soon you'll be able to get an actual reading in ppm on the controller. The page you select "float" or "analog" for a specific sensor will have other options such as Air CO2, anything that'll work on those ports.
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I was thinking it was some thing like that. have you tried to run the skimmer intake airline out side some how even if it is just a temp thing to see the effect on your tank
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