I have tried to see how well the various methods work for measuring CO2.
In a nut shell, even if your KH is off, weird, not accurate etc........the pH meter should get you pretty close(about as well as a 2500$ meter).
Now this is not to say that the aquarium will be the same in all cases and that the degassed aquarium will be the same, they will be if you have a wet/dry and good surface skimming.
I used a flat tip pH probe and rubber grommet and used maybe 300-400ul of KH reference solution 4KH(71.44ppm) and managed to get the air bubbles out. PITA.
I think a simple manufacturer made slip on cap would do well/better and be cheap. I spoke to American Marine about this a couple of years ago. Not much has come of it.
This compared very well vs the Oxygard CO2 meter. I needed to compare these two items against a standard American Marine pH meter (one of the oldest brands and still pretty good, easy to use etc) with the flat tip KH reference cell.
I measured the KH in my tank water carefully using 2 different methods and they matched to the ppm and the reference measure at 71.4 matched within 1ppm.
So my tank's all have the same KH, in this case 37ppm.
Typically from about Dec-June it's 20ppm, the water companies struggle to keep it up due to the new water from snow and rain.
My non CO2 tank measures : 7.58 to 7.60 pH
The 120 gal measures about 6.1 late in the day
The 70 Gal measures 6.01 midday
The 180 measures 5.90
There is likely little influence on KH from non bicarbonate alkalinity.
So the pH/KH chart works in MY CASE right now.
I do large water changes, I also have mature older wood and ADA Aqua soil.
The other question is while the meters all read very close to the same and the KH etc.........
I want to be sure, so I made some CO2 solutions with some flask and rubber stoppers.
I used Distilled water with a conductivity of 0.9uS(very pure) and added enough KH to get 17.8ppm and made 1 liter.
I chipped off 53 ppm of CO2 dry ice and weighed it right before I added(51 mg to 1 liter of water) it to the flask and sealed it. I was careful, not to have any air bubbles after sealing(after 6 attempts).
I placed this on the magnetic mixer and the rubber top has a 1/2" pH probe gasket. I wait about 15 min and then take the reading.
6.10-6.09. Pretty darn close. pH meter and probe are new and they were calibrated right before this was all done.
This is also about the same range the Flat tip with the KH reference cell came up with using this same method(4 attempts, see? I was getting better).
So that CO2 meter worked well and had relative fast response times in under 5min.
Next, I want to see if I can detect low CO2 in the plant beds in the low flow regions vs the high flow where the CO2 comes in etc using just the pH meter.
I predict I can.
Some discussion comments:
Verification of the method and using a reference sample is a challenge.
Many plant hobbyists have long gotten away from using a pH meter to adjust and watch their CO2.
KH uncertainty can varied and can be large depending on tap water sources
Wet/dry/surface skimming methods will give the best degassing after the CO2 is stopped being added at night.
Canister filters will retain the CO2 and surface scum also appears to contribute to this issue, the latter perhaps the majority.
In general, do not assume anything, verify and double check, particularly if some thing is going REALLY well, and if something just seems off.
The filtration issue alone/degassing rates etc, make the pH meter a problem for some, but easy as pie for others.
The tap water KH with non alkalinity makes life tougher for some people, but , you should be able to use a KH relative measure based on a degassed sample(or if you have a wet/dry and surface skimming, then add CO2 during he day time only.....) and add CO2 to get the appropriate scaling needed to target say 40ppm or 20ppm or 30 ppm etc.
When I did this, I noticed I'd not adjusted the timer correctly for the only problem tank I have which is the 70 Gal manzagumi. So I was able to catch that and adjusted the timer to account for the lighting time.
For all the verification, it's the simple stuff that gets me time and time again, so I know not to trust myself and feeble mind and instead, need to go through and check things one by one.
And if it gets me, then there's certainly going to be a good sized chunk of the public that also gets nailed.
and not just the "new" folks either...........
In a nut shell, even if your KH is off, weird, not accurate etc........the pH meter should get you pretty close(about as well as a 2500$ meter).
Now this is not to say that the aquarium will be the same in all cases and that the degassed aquarium will be the same, they will be if you have a wet/dry and good surface skimming.
I used a flat tip pH probe and rubber grommet and used maybe 300-400ul of KH reference solution 4KH(71.44ppm) and managed to get the air bubbles out. PITA.
I think a simple manufacturer made slip on cap would do well/better and be cheap. I spoke to American Marine about this a couple of years ago. Not much has come of it.
This compared very well vs the Oxygard CO2 meter. I needed to compare these two items against a standard American Marine pH meter (one of the oldest brands and still pretty good, easy to use etc) with the flat tip KH reference cell.
I measured the KH in my tank water carefully using 2 different methods and they matched to the ppm and the reference measure at 71.4 matched within 1ppm.
So my tank's all have the same KH, in this case 37ppm.
Typically from about Dec-June it's 20ppm, the water companies struggle to keep it up due to the new water from snow and rain.
My non CO2 tank measures : 7.58 to 7.60 pH
The 120 gal measures about 6.1 late in the day
The 70 Gal measures 6.01 midday
The 180 measures 5.90
There is likely little influence on KH from non bicarbonate alkalinity.
So the pH/KH chart works in MY CASE right now.
I do large water changes, I also have mature older wood and ADA Aqua soil.
The other question is while the meters all read very close to the same and the KH etc.........
I want to be sure, so I made some CO2 solutions with some flask and rubber stoppers.
I used Distilled water with a conductivity of 0.9uS(very pure) and added enough KH to get 17.8ppm and made 1 liter.
I chipped off 53 ppm of CO2 dry ice and weighed it right before I added(51 mg to 1 liter of water) it to the flask and sealed it. I was careful, not to have any air bubbles after sealing(after 6 attempts).
I placed this on the magnetic mixer and the rubber top has a 1/2" pH probe gasket. I wait about 15 min and then take the reading.
6.10-6.09. Pretty darn close. pH meter and probe are new and they were calibrated right before this was all done.
This is also about the same range the Flat tip with the KH reference cell came up with using this same method(4 attempts, see? I was getting better).
So that CO2 meter worked well and had relative fast response times in under 5min.
Next, I want to see if I can detect low CO2 in the plant beds in the low flow regions vs the high flow where the CO2 comes in etc using just the pH meter.
I predict I can.
Some discussion comments:
Verification of the method and using a reference sample is a challenge.
Many plant hobbyists have long gotten away from using a pH meter to adjust and watch their CO2.
KH uncertainty can varied and can be large depending on tap water sources
Wet/dry/surface skimming methods will give the best degassing after the CO2 is stopped being added at night.
Canister filters will retain the CO2 and surface scum also appears to contribute to this issue, the latter perhaps the majority.
In general, do not assume anything, verify and double check, particularly if some thing is going REALLY well, and if something just seems off.
The filtration issue alone/degassing rates etc, make the pH meter a problem for some, but easy as pie for others.
The tap water KH with non alkalinity makes life tougher for some people, but , you should be able to use a KH relative measure based on a degassed sample(or if you have a wet/dry and surface skimming, then add CO2 during he day time only.....) and add CO2 to get the appropriate scaling needed to target say 40ppm or 20ppm or 30 ppm etc.
When I did this, I noticed I'd not adjusted the timer correctly for the only problem tank I have which is the 70 Gal manzagumi. So I was able to catch that and adjusted the timer to account for the lighting time.
For all the verification, it's the simple stuff that gets me time and time again, so I know not to trust myself and feeble mind and instead, need to go through and check things one by one.
And if it gets me, then there's certainly going to be a good sized chunk of the public that also gets nailed.
and not just the "new" folks either...........
!