I'm not a chemist and this is only my second post around here, but I'm curious about this. Why are you bothering with membranes? Couldn't you mount the sensor in a container above the water's surface but open to the water. The concentration of CO2 in the air space should reach equilibrium with the concentration in the tank water. Then you could use Henry's Law to calculate the concentration of CO2 in solution.
Caq/Cgas = 0.8317 for CO2 @ 25 C
Yup that's an option as well. If water floods the electronics, we have an issue. The membrane is a safer solution and responsive solution.
It's worth a try though.... Maybe the sensor can hang from the tank. Depending the the design, it could be affected by ambient co2 or slow in response. It's pretty amazing how much co2 increases when there are people around the sensor. You can use it to detect people.
I'll give it a try down the road.
Last edited by mistergreen; 12-16-2012 at 04:49 PM.