I was looking and have been for some time, for various responsive methods to measure CO2 in water.
Most methods involve some transition from water to the air. We add gas, then it dissolves(we assume all of it), then it gets to the plants or off gases to the air above.
Test kits, pH meters, colorimeters, drop checkers, and color charts are not that reliable.
We also have O2 and light PAR issues, so even say 30ppm might not be enough or might be too much depending on those 2 parameters.
Still, I'm looking for some reliable method that would yeild +/- 1ppm or within 1ppm. Needs to be cheap and perhaps integrated into a controller type function.
I think I've found a good method that's within 200-600$ range.
Takes a little DIY and is a bit like a large Drop checker in some ways. I'd still need to verify it against a reference to be sure the method is accurate and responsive.
Method 1:
pH reference cell across a membrane is one method(Basically the KH ref of 4 degrees is used to wrap the pH probe tip) and using the selective gas membrane to keep the KH solution in, but allows CO2 and other dissolved gases across.
Method 2:
Using a relative inexpensive air/gas IR analyzer to measure gas CO2 inside a bell that is inverted with a gas bubble at the top to withdraw the degassed tank water. No it will not be 30ppm in the bell
1500-2500ppm is more the range for us.
This method also allows very low levels of measure with high accuracy. It as well as method 1 are still limited by Fick's 1st law of diffusion across the boundary layer between gas/liquid phases.
Since the gas does need to go back into solution like in the Drop checker, the response is faster, and with a larger bell, we can get faster response times and a more even average of the tank since the area is much(can be). the gas IR can measure fast and very accurately, as well be linked to a controller function. It typically uses the air as a reference to self calibrate.
These run 200-600$ or so on line.
The bell collection needs DIY'ed to the tank and then a sample hole that's sealed needs added to the gas bubble area.
I'm not sure it would work, or not.
Seems like it would be worthwhile to do/try.
Using degassed CO2 seems like a good method and has much higher % accuracy and the ppm's are much higher for gas. You could also use O2 for this method as well if you used an O2 gas analyzer.
They also make human health CO2/O2 analyzers that might be able to do the trick for both CO2 and O2 pretty accurately in liquid/gas phases perhaps.
Regards,
Tom Barr
Most methods involve some transition from water to the air. We add gas, then it dissolves(we assume all of it), then it gets to the plants or off gases to the air above.
Test kits, pH meters, colorimeters, drop checkers, and color charts are not that reliable.
We also have O2 and light PAR issues, so even say 30ppm might not be enough or might be too much depending on those 2 parameters.
Still, I'm looking for some reliable method that would yeild +/- 1ppm or within 1ppm. Needs to be cheap and perhaps integrated into a controller type function.
I think I've found a good method that's within 200-600$ range.
Takes a little DIY and is a bit like a large Drop checker in some ways. I'd still need to verify it against a reference to be sure the method is accurate and responsive.
Method 1:
pH reference cell across a membrane is one method(Basically the KH ref of 4 degrees is used to wrap the pH probe tip) and using the selective gas membrane to keep the KH solution in, but allows CO2 and other dissolved gases across.
Method 2:
Using a relative inexpensive air/gas IR analyzer to measure gas CO2 inside a bell that is inverted with a gas bubble at the top to withdraw the degassed tank water. No it will not be 30ppm in the bell
1500-2500ppm is more the range for us. This method also allows very low levels of measure with high accuracy. It as well as method 1 are still limited by Fick's 1st law of diffusion across the boundary layer between gas/liquid phases.
Since the gas does need to go back into solution like in the Drop checker, the response is faster, and with a larger bell, we can get faster response times and a more even average of the tank since the area is much(can be). the gas IR can measure fast and very accurately, as well be linked to a controller function. It typically uses the air as a reference to self calibrate.
These run 200-600$ or so on line.
The bell collection needs DIY'ed to the tank and then a sample hole that's sealed needs added to the gas bubble area.
I'm not sure it would work, or not.
Seems like it would be worthwhile to do/try.
Using degassed CO2 seems like a good method and has much higher % accuracy and the ppm's are much higher for gas. You could also use O2 for this method as well if you used an O2 gas analyzer.
They also make human health CO2/O2 analyzers that might be able to do the trick for both CO2 and O2 pretty accurately in liquid/gas phases perhaps.
Regards,
Tom Barr