How to monitor CO2?

[priv_sim]

Hello,

I was searching for this all around aquarium forums, but I have just found bits n pieces for this question. Would be nice if someone could explain/sum up this problem:

Is there some kind of way to monitor dissolved co2 fluctuation in real time? I am guessing frequent Ph testing should tell me something, but what I should aim for? Also how to use kh/ph table more accurately (lets say my water is 13dKh and 7.2 Ph)?

Thanks a lot!

 

[Darkblade48]

If you want instantaneous results, then the only way you can measure CO2 fluctuation is with a CO2 meter. These can be expensive.

The cheapest way to monitor CO2 is to use a drop checker with a 4 dkH reference solution. With a known carbonate hardness, as well as an indicator that turns colours at fixed pH (in this case bromothymol blue), you can figure out the concentration of CO2 in the water.

However, a drop checker takes about 1-2 hours to react to the amount of CO2 that is in the water. Essentially a small air/water interface allows CO2 to degas from the water into the small air space, which then diffuses back into the liquid that is in the drop checker.

Unfortunately, measuring the pH and the kH of aquarium water and then calculating CO2 does not really work, since there can be other factors that will contribute/affect kH, resulting in skewed results.

 

[priv_sim]

How about testing just ph levels with electronic ph meter? I wont be able to see concentration of dissolved gasses, just fluctuation - that would help to establish stability.

About kh/ph table, is it possible to adjust it to specific water parameters?

 

[Darkblade48]

Testing your pH with an electronic device will eliminate problems with repeatability, but still does not make the other unknown variable (kH) known, so the relationship cannot be used unless you know exactly what/how much is contributing to kH and adjust accordingly.

As mentioned, if you are only looking to establish that you have a steady CO2 supply, a drop checker will do that; it just has a time lag of 1-2 hours before enough gas diffuses in/out of the drop checker solution to give a colour change.

 

[krandall]

My personal feeling is that I'd rather check pH using a normal pH test kit with bromothymol blue, rather than keep a drop checker, as just one more piece of equipment in my view in a display aquariums. I don't have anything in my tap water that is going to skew the KH reading so far that I can't make a reasonable "guestimate" about CO2 concentration. I use the pH test to initially establish a reasonable bubble count for the specific tank. Then I use a combination of checking the bubble count and watching my plants' reaction to determine whether I am supplying enough CO2.