Affordable CO2 sensor?

[mistergreen]

hmm. have to check out the tyvek material. Wow, silicone membrane is expensive.It's probably the best for this purpose. I can probably make it for now. Silicone peels off wax paper pretty well.

[Wasserpest]

Have you been able to confirm real world things, like CO2 fluctuations between day and night in your low tech tank?

[mistergreen]

Originally Posted by Wasserpest

Have you been able to confirm real world things, like CO2 fluctuations between day and night in your low tech tank?

I'd have to write an app to log the data which wouldn't be hard. I wouldn't be interested looking at numbers all day long
Actually, I just finished up a project and will have time to write up an app.

I have confirmed different CO2 levels in different tanks.

1. tub of tap water - 4.6 ppm
2. low tech in the morning - 20.18 ppm
3. hi-tech at peak levels (afternoon) - 44.01 ppm

[mistergreen]

ok, just finished the app. I modified an app I wrote for the PAR sensor. I will run it tomorrow morning. I'll have it log every hour to a text file instead of every second which the CO2 sensor sends to the output pins.

[mistergreen]

For fun, I ran the app. The lights are off in my low-tech.

There's a time stamp (h:m:s) with the co2 ppm.

log.txt

19:7:47 -

Serial Up!

19:7:47 -
Co2 ppm = 10.01

20:0:0 -
Co2 ppm = 11.05

21:0:1 -
Co2 ppm = 12.16

22:0:0 -
Co2 ppm = 12.88

Looks like the trend is the CO2 builds up till the lights turn on. Who knew there was a natural CO2 generator in my tank .... Actually, I knew.

[mistergreen]

I let the log app running all day. Here are the results.
Lights on at 9:35:0
Lights off at 17:35:0

9:24:59 -
Co2 ppm = 18.70

10:0:0 -
Co2 ppm = 18.64

11:0:0 -
Co2 ppm = 18.03

12:0:0 -
Co2 ppm = 17.48

13:0:1 -
Co2 ppm = 16.76

14:0:0 -
Co2 ppm = 16.22

15:0:1 -
Co2 ppm = 15.81

16:0:1 -
Co2 ppm = 15.61

17:0:0 -
Co2 ppm = 15.43

18:0:0 -
Co2 ppm = 15.33

19:0:1 -
Co2 ppm = 15.61

20:0:0 -
Co2 ppm = 16.01

CO2 fluctuates with the lights. Pretty interesting. The swing is minimal so I'll use that as a model for the hi-tech tank. CO2 turns off at say 40ppm and back on at 35ppm. I'll probably wear out the solenoid with the constant switching. Peak CO2 should be when the lights are on also like the low tech, maybe that's the secret to BBA.

[mistergreen]

I made my own silicone membrane between 2 pieces of wax paper.


It's 1 mm in thickness about 3x as thick as the breather bag. It's also twice as reactive allowing about 2ppm per minute.

I also finished building the relay connections and will hook it up later today. I'll run for a month and observe fish reaction and BBa.

** oh, I just figured there's a mathematical limit to this sensor. You can only read 0 - 44.01 ppmw (this is what we want) and 0 -10,000 ppmv. It's good for growing plants. I probably had higher CO2 levels in my tank. I thought it looked suspicious that it stopped at 44.01ppm every time. I knew there's a reason why my fishes were so skittish.

[Hoppy]

Originally Posted by mistergreen

I made my own silicone membrane between 2 pieces of wax paper.


It's 1 mm in thickness about 3x as thick as the breather bag. It's also twice as reactive allowing about 2ppm per minute.

I also finished building the relay connections and will hook it up later today. I'll run for a month and observe fish reaction and BBa.

** oh, I just figured there's a mathematical limit to this sensor. You can only read 0 - 44.01 ppmw (this is what we want) and 0 -10,000 ppmv. It's good for growing plants. I probably had higher CO2 levels in my tank. I thought it looked suspicious that it stopped at 44.01ppm every time. I knew there's a reason why my fishes were so skittish.

Wow, that is really carrying DIY to an extreme! Could you make a membrane about a tenth as thick? A mm seems much too thick to get fast response. Could you provide some details about how you made the membrane?

I don't think 44 ppm is high enough as an upper limit. I know Tom Barr has used higher levels of CO2 for some of his tanks, without sacrificing fish as a result. I think about 60 ppm would be the minimum desired max limit.

[mistergreen]

I tried making it thinner but it was impossible remove in one piece. Well at least it's better than the breather bag. I also have a big sheet of vytek. I'll try that later. Making the silicone membrane was easy. A glob of silicone between wax paper and a rolling pin or in my case a wine bottle. Let cure for a few days and peel slowly of one piece and then let it cure completely.

I just did some equipment check and was trying to figure out why the relay wouldn't trigger the solenoid. It turned out the water still had 44+ppm of co2 in it. This is 6 hours after lights out.

I'm going to stay with ranges of 35- 40 ppm. My fishes just aren't happy with the amount I've been pumping in and BBa isn't completely eliminated. I've put the sensor farthest from the outtake so some area will be more than 40 ppm I'm sure.

Can you imagine the amount of co2 we're pumping into these tanks? Over 33x the amount in air.

I'll check the co2 sensor manufacturer if they make something higher than 10,000 ppmv.
**** they do make a 30,000ppm and a 300,0000 ppm model but they're $250.

The 30,000 module should work. The maximum value is 132 ppmw.

[mistergreen]

I just point my spray bar straight up. That should allow more o2 into the water.

[mistergreen]

Darn it. I need a rigid screen under the membrane. The water pressure pushed the membrane against the air ports and skews the readings. That's why it was at maximum the whole time.

I didn't have this problem in the 10g because the water pressure wasn't as great.

[mistergreen]

tyvek fabric is not water proof
Under pressure, water goes through the pores.

[Darkblade48]

Originally Posted by mistergreen

tyvek fabric is not water proof
Under pressure, water goes through the pores.

The electronics were not damaged, I hope?

[mistergreen]

Well, this sensor is pretty rugged. It had been wet a few times. As long as I pull the power before any burning, it's fine.

Back to using the breather bag.

[mistergreen]

Ok, everything is hooked up. The relay is hooked up to the arduino. It's on a timer as well.
In the future the timer would be integrated with the arduino.

The current reading is 11.57ppm.

I'll try to make another, thinner silicone membrane. I'll throw it in the oven this time (150F). I hear silicone cures faster in heat. The wax might melt on the silicone but I can remove it with a paper towel and an iron.