yme;62634 said:
hi!
this concerns me!!
What would you advice me to do?
I calibrate once every 2-3 months or so. I find never a big difference between before and after calibration. 5 ppm at most.
I don't have N2 at home, so this method is not an option.
The pH/KH scaling seems most feasible to me.
However, how can I do this in practice?
Making the KH-solution is of course no problem.
But how can I add CO2 , mix it using a stirring bar and measure both CO2 and pH at the same time? (and don't make errors due to the slow respond time of the CO2-probe)
I don't really see yet the setup of this method.
thanks!
yme
Well, after looking at it, they also have issues with this also.
It's not easy for them to offer a user freindly method.
So I understand.
I tried 3 different methods to verify, not satifisied with their method for calibration myself.
If you can construct a nice large drop checker and can withdraw a smaple with a suction bulb, and have areference KH solution and a pH probe calibrated well in this water, and sealed, you can allow for a long time to pass and equilibrate.
Unlike a drop checker 2 huge trade offs, the time delay and the poor accuracy of pH, this is over come.
The reference solution is all pure water and sodium carbonate reference solution.
Since time in not really important for calibration, this can be allowed to equilibrate for 24-48 hours etc.
Then take a highly accurate pH reading.
This reading can then be used to adjust the slope of the CO2 meter.
You may/should also vary the CO2 content for the sample test water.
So try to test a low(no CO2 added), then med, say 30ppm and then say 60ppm.
Compare this reading to the tank's pH and KH reading, see if they match.
If so, you have few interefearing KH factors and can use the pH/KH relationship.
That was the case here, since they change water very often and use RO/blended with a little tap.
You can make these chambers out of acrylic, then add a rubber grommett for the pH and then another for the CO2 probe.
I think it would be even better to allow plenty of time, but add CO2 gas to the air in the dry part of the chamber to change the concentration vs the way I did it, which was a PITA.
Still, with a known KH and a pH meter, we should if the water is oure and only HCO3..be able to dial in a reference CO2 ppm to 1ppm or less perhaps.
There's another company that makes CO2 systems for ultra pure water, they go to the ppb range they say, seeign their claibration methods might be interesting, still, I like the IR for gas, then convert that from the seal chambers to ppm for aquaous solutions for the gas in the head space.