Originally Posted by tiger15
What co2 sensor do you use? I much prefer direct measurement than kH pH guessing.
It depends on your needs and price points. https://www.co2meter.com/collections/co2-sensors
You'll have to build a waterproof casing for it and allow for a CO2 gas membrane. I used a thin silicone membrane. It works ok for the price. There are better membranes like PTFE, Polytetrafluoroethylene but they're very expensive. Water molecule can enter as well so if it gets too humid, you have to open it up and let the humidity out.
Be aware these measure in ppm by volume. In water, it is by weight (smaller number to deal with).
10,000 ppmv is 17.99 ppm(weight)
You'd want 30,000 ppmv or 100% sensor to measure higher values.
I use this formula to convert
ppmw = ppmv×44.01÷(0.08205×298.15)÷1000
44.01 is mol weight of CO2
0.08205 is a gas constant
289.15 is 77F in Kelvin
1000 is density of water
They have a Windows software for you to collect the data or you can hook it to an Arduino for remote data logging.