Co2 drop checker vs ph measure

[hax47]

I mostly think the usually accepted low-tech CO2 value of 2-4 ppm is just wrong actually. I'm reasonably sure a drop checker using a 0.25 dKH bromothymol blue pH indicator solution would do a pretty good job of sorting out these lower CO2 concentrations, but making such an indicator solution correctly would not be a trivial undertaking.

Using an equilibrated bicarbonate solution and pH measurements, I couldn't measure levels much below 1.6 ppm indoors during the summer (when the house is likely better ventilated). Typically, I get values between 2 and 3 ppm. On the porch, I could measure as low as 0.65 ppm, which is much closer to equilibrium with atmospheric air. However, this is specific to my home, and as we see, the CO2 concentration is somewhat elevated there; it may vary in other households.

 

[Mattsdoneitagain]

It's a tangled mess, but it doesn't need to be.

The best advice I can give to anyone starting out injecting C02 is this.
Use 3 methods of calculating co2 levels. Ph change, drop checker colour, and the most important measure by far... how are the fish reacting.

Ph meters are accurate enough for our needs, the ph change is the important bit. Whether or not it was lab grade calibrated is imo, a distraction.
Monitor the ph and look at the dc, make photographic notes how the dc changes in relation to the ph. Obviously understand the dc lags by 1 ~2 hrs.

By doing this you will quickly learn to guesstimate the tank ph based on the dc colour, or guesstimate the dc colour based on ph meter readings.

I've just eyballed both dc' in my tank, I guessed one was sitting at 6ph, the other at 5.5. I wasn’t that far out. 😆

View attachment 217180View attachment 217181

View attachment 217183View attachment 217182

That’s exactly what I have done 👍 so I’m definitely in the ball park
Thank you

 

[aquanoobie]

Unless you keep the aquarium outside in the backyard, you probably will never have 0.6 ppm equilibrium CO2 in the aquarium (which value corresponds to about 400 ppm CO2 in the air). Here are some recordings from a project in progress... Continuous CO2 measurements in room air where I keep some of my aquariums. The room CO2 levels touch the 600 ppm range only for a short period when no one is at home, otherwise, it resides over 1000 ppm:

Does it impact the final 1 pH drop CO2 water concentration depending on what hour was the degassed water pH reading taken?

 

[aquanoobie]

There is no pH dependence on the ratio of dissolved CO2 to carbonic acid.

Is the ratio KH dependent?

 

[hax47]

Does it impact the final 1 pH drop CO2 water concentration depending on what hour was the degassed water pH reading taken?

The water equilibrium with the air is a relatively slow process, so the water CO2 swings are probably smaller, I expect the water CO2 to be some kind of a moving average of the CO2 equilibrium. So it means that the 10x CO2 after a 1 pH drop will not be exactly 30 ppm, and will be affected by the time it is measured. But I don't think that the CO2 has to be set very precisely.

 

[Andy Pierce]

Is the ratio [of dissolved CO2 to carbonic acid] KH dependent?

Short answer is no.