Gas-exchange experiments

[Andy Pierce]

You could add HCl to tap water and pour it into the tank, it will not lose the CO2 that quickly. But then you could just make fresh soda water and use that.

I used to use HCl this way as a temporary CO2 booster, but have abandoned that approach.

If the goal is primarily to temporarily add dissolved CO2 to the tank then making fresh soda water and adding that makes sense to me (although just directly injecting CO2 gas is my preferred approach). Presumably you could even pull some water out of your tank and carbonate that. For me the main reason for adding HCl is to permanently decrease the alkalinity. In fact, when I add HCl to tap water before a water change now I subsequently degas the treated water before adding to the aquarium to remove the excess dissolved CO2 so the pH won't be too different - as noted previously an acid-caused decrease of 1 dKH only changes the pH by less than 0.1 units after gas equilibration but by considerably more than that before equilibration. Unlike adding carbonated water where your potential to go dramatically wrong seems pretty limited, I expect you need to be a lot more careful about HCl addition to be sure you don't run all way out of (bi)carbonate and crash your pH.

 

[PeerUnk]

My well aerated tank follows the ambient room CO2 levels pretty accurate.

Well, I need to edit this statement I made. After successfully installing my own pH sensor, the CO2 could not be following the ambient room CO2 reading that close with heavy aeration; The pH (and therefore CO2 readings as it is fixed to the KH) was much more stable.

I found out I had a air leak in the gas chamber next to the sensor. So the CO2 reading was actually following the ambient room CO2 level, only not via the water of the tank, but via the air leak.

So I fixed it and the CO2 reading is much more stable as the pH reading is. Below the last 36 hours. The yellow trend is the CO2 in the gas chamber and therefore of the water. And it is reacting slower on the increase of the ambient air CO2 measured at the air pumps (green line) The pH in orange is faster in it's reading, following the ambient CO2 reading in (green) and increase in pH affected by the uptake of CO2 by the plants during lighting (in blue):

converting those reading all to CO2 in the water, the trends are even more obvious. I deleted the actual readings, as re-calibration still needs to be done:

After calibration I will conduct the soda bottle experiment.