Drop checker is a nifty invention and I take my hat off to thinking people who put 2 and 2 together and come up with inventions like that.
Drop checkers are visual aids at a very reasonable price and they provide an approximation of co2 concentration. To measure the co2 concentration in water more accurately currently requires more technology with a ~$2,000 price tag to start. Understanding how drop checkers work and their limitations helps us to set our expectations on what we actually get for $25 and how to use them to our best advantage.
The basics are rather simple (and beatiful): you have a liquid with known properties (aka reference solution which is usually RO water with 4 dKh). The reference solution is then mixed with several drops of pH reagent. The chemistry tells us that by adding co2 to that solution will drop the pH (CO2+H20 -> H2CO3). The drop in pH will change the color of the solution in a known fashion (blue to green to yellow) due to the reagent. Because we are dealing with known quantaties, the conversion of color to co2 concentration is calculatible (and rather linear).
The mixture goes into a small chamber with a very narrow neck (to prevent tank water from getting in). When we put a drop checker in a tank, we create an almost closed system:
Reference solution in a glass / plastic (i.e. non-porous) chamber -> atmospheric air acting as a water barrier -> tank water.
Taking a step back, we examine our system to think about what we got:
- the solution is "isolated" and (theoretically) the tank water does not get mixed in
- for anything to get to the solution has no place to come from but from the tank water
- for anything to get to the solution it has to be in gaseous form to get through the air barrier
Therefore, the basic idea here is that co2 (gas) escapes from the tank water into the drp checker. The color of the drop checker will change based on how much co2 makes it to the solution. Brilliant, imho.
And that's the theory, as I understand it. All nice and well.
Now, to all the thinking people out there, why this nifty, scientifically backed-up tool:
- would "lie"?
- what are the limitations?
- why is it analogous to a, say, a chain saw?
In conjuction with before mentioned post https://www.plantedtank.net/forums/26...er-works~.html
, I hope my monolog will provide more food for thought.
PS: to add more wood to the fire, concentrations of co2 at that "magic" 30 ppm and above are possible. But I content that the probability for most of us actually getting to that 30 is rather slim, regardless of what your drop checker tells you.