AquaticTechTank.net

You're spot on with it all.

I realized I made a mistake, one I avoided elsewhere. ABC adjusts up to 30ppm/week - but in air, not water - so this is ppmv. As 400ppmv in air is about 1.3ppmw in water, the weekly impact of ABC in measurement of water CO2 content is then 30/(400/1.3)=0.0975ppmw. That is, if I haven't made another mistake, hehe. MUCH more reasonable than the 30ppmw error I was originally worried about.

As for the pricing difference between 1% and 3%, I'm not ruling out the possibility it's an artificial increase rather than more costly precision hardware. It works on this principle:



Since the light absorption of CO2 is tiny, I'm thinking it should be easier to detect at higher ppm, not less. I'd be curious if there are any visible component differences on the circuit side between the 1% and 3% versions.

I also visited the manufacturer's website, rather than co2meters. Where I was able to download the software included in the dev kit for free:



And although I don't have a sensor, I was able to get this screenshot:



So it appears the $10 extra for the "custom" 1% sensor, is just a charge for co2meters hooking up the sensor and setting this for you. With the purchase of a dev kit (or maybe just a cable), you could do the same, probably even on the 3% sensor. There are other options too, it's possible you might be able to extend the range of the 1% sensor somewhat.

I happened across some other NDIR sensors too:



Only good up to 2,000ppmv (6.5ppmw?). But at only $10, it might be fun to take apart and see how it works. Or try to modify it for a higher range.



$65, good up to 2% (20,000ppmv). Or 3.2% via UART only, with reduced accuracy. The sensing part seems to be sealed, with a gas diffusion membrane built-in. Could possibly be a superior choice, though I haven't read the datasheet fully enough to know if there's any catch.

The 3% sensor arrived over the weekend.



I gave DIY silicone membrane a try. It's a little thinner than the commercial silicone sheet I bought. I started to notice condensation forming in the open version.




I saw a discrepancy in the code/readout. I believe for the 3%, all readouts have to be multiplied by 3. I'll see if this is the case tomorrow when the CO2 kicks in.

Oh, and it does look like the 3% is related to the 1% sensor. Somebody should be able to hack the 1% somehow.

They both have a range of 0-10,000. The only difference is the readout of the the 3% is reduce by 1/3.
So if the 1% reads 600ppm, the 3% will read 200ppm.

So in the code, you multiply the values of the 3% by 3 to get the correct value. So, the max value of 30,000 is really 10,000 in terms of output.

Hmm... I don't see any mention of updatable firmware, which could make it super easy to hack after comparing firmwares for both sensors. May still be possible if someone can locate a JTAG port.

Great work so far!

I think the 1% is good enough for the hobby. I tried controlling the co2 up to 40+ppm with the 3%, and the fishes started to act funny. I now don't believe stories of people having 60ppm and the fauna are fine and dandy. You know who they are

They're probably overestimating or created so much surface agitation that the co2 never gets a chance to stay in the water for long.

It's cool to see this sensor is more reactive than a drop checker. It takes hours to see a color change. I'm sure there's a lag with the sensor. I'm thinking 15 minutes at most.

I believe it's possible, at least in some instances, to run at 60ppm without affecting fish. Did it once by accident.

But I don't think it's necessary. I've been running 20ppm for a couple of months now in a high light tank, without noticeable consequences. In my opinion, 30-40ppm really should be enough for anyone. Any more than that is probably overkill, overestimation of the actual level, or using CO2 to make up for other issues which should instead be directly addressed.

If there is significant demand for higher range measurement anyway, that S8 sensor I earlier linked looks to be a more economical alternative than the K-30 3%.

My code failed me today. The CO2 level was up to 91ppm and the bottom dwellers were on there sides. I quickly did a 50% water change and brought the level down to 51ppm.

I simplified the on/off condition. I'll update all of the code listed so far. Whiles repairing the code, the flying fox decided to make a break for it and jumped out of the tank and landed next to the laptop.

I do applications work at CO2meter.com and came across your group discussions regarding Aquatic CO2 measurement..
Just a note about the ABC (automatic background calibration) function on the CO2 sensors.
If you set the ABC interval to 0 ABC is disabled. ABC is purely for IAQ (Indoor Air Quality) applications.
The value is store in EEPROM, you can access and modify teh configuration of the sensor with the DAS software the you can download from the CO2meter.com website.