Thoughts on light levels and co2 loss with power filters

I think it is safe to assume that they are using 4 dKH water with bromothymol blue indicator solution in the measuring portion, and I assume they use a known pH 6.6 buffer solution with the same indicator in the reference portion. That would be a 30 ppm "good CO2" level. The way they made it, the reference portion is also a drop checker, so the buffering ability would have to be very high (?) to avoid the CO2 in the tank water from affecting the color. The way I was going to make that was to seal up the reference solution to keep the tank water CO2 out of it.

 

The reference solution is in a totally separate bulb, with its own small diameter entrance, with that as an air gap. Look at the photos on that web page very closely.

 

I didn't think buffer had any effect on pH changes due to co2 addition.

 

We generally misuse the term "buffer" to mean having a high KH. Buffered solutions generally are a mix of an acid and one of its bases, such that the mix maintains a fixed pH with small additions of acids and bases. But, knowing how to "make" a pH 6.6 buffered solution is outside of my knowledge bank. I have read numerous descriptions that are supposed to say how to do it, but I just don't understand what I read.

The KH in our aquarium water doesn't prevent a change in pH when an acid, such as carbonic acid is added, or at least I don't think it does. In any case, for that new drop checker reference system to work, it has to truly be buffered, so the CO2 that will get into that bulb does not affect the pH.

 

I don't know, but they emailed me very promptly after I ordered, so I suspect they would answer an emailed question equally promptly.

I emailed them just now to see if I am correct. I will post their answer.

 

Here is their answer: (less than 3 hours later!)
"Your assumption is on the right track. A buffer is the main ingredient in the reference solution plus some stabilizers.
The included solutions should last you close to a year. We do plan to provide larger quantities (~100 ml) available in the near future. Definitely before the included ones run out "

 

Thanks, I learned something today.

 

They didn't deny that the reference solution contains the same indicator and the pH of that solution is 6.6, with corresponds to 30 ppm if the KH is 4 dKH.

If the known KH solution is 2 dKH, the 6.6 pH indicates about 15 ppm. Since it is obvious that CAL AQUA picked up the drop checker idea for measuring CO2, as opposed to measuring tank water pH, from these forums, where I started the ball rolling, it is very unlikely that the target ppm is anything but 30 ppm. However, you could always make your own known KH solution and pick one that gives whatever CO2 concentration you want at 6.6 pH. The indicator reagent is almost certain to be bromothymol blue, the only pH indicator that indicates in the range of interest with clear color changes.

 

Perhapes the reference solution color is food coloring. Would it settle and clear after a while?
Just an Idea. I don't know chemistry.
Joe

 

No, it isn't food coloring. They confirmed that it is a buffered solution, held at 6.6 pH, with some "stabilizers" added. On TPT forum they confirmed that the CO2 concentration this is aimed at is 30 ppm.