Over the past six months I've been trying to grasp co2 levels in my two tanks (40b and 20H). I have devised this method of using a drop checker to get accurate levels of co2 based on evidence collected from the following sources:
-Fish Health (A subjective piece of data. Includes breathing heavily, and overall activeness)
-Ph readings using a digital probe
-kH readings using API drop method
-Color of drop checker using 4dkh solution
Piecing together these bits of info into an overview of current co2 levels is challenging, but overall not impossible. I hope this essay can help those who find obvious signs of co2 deficiency in their plants, but have a yellow drop checker.
Before I go into methods and discussion, I need to qualify that this article will have little relevance when a tank is using a reactor because almost all of the co2 is dissolved, and not in a gaseous form (bubbles). Perhaps another reason why a reactor might be a better choice....
Involves using a drop checker and a ceramic diffuser. Moving the drop checker away from the diffuser's bubble stream, or the co2's point of origin (PoO). A powerhead spitting out impeller-chopped bubbles can be used as well.
First, the differences between actual dissolved co2(aq) and bubbled(gaseous) co2(g) is of consequence when measuring co2 via a drop checker. If co2(g) is allowed to sneak into the drop checker's point of access, a bad reading will be obtained when the checker is viewed.
Test this by putting the drop checker's access point directly under the co2's PoO. Tons of micro bubbles will go into the drop checker and make it turn yellow very fast. However, this result doesn't reflect what the actual dissolved co2 levels are in the tank.
Test the color of the drop checker as it moves further from the PoO. The color will change until eventually no co2 bubbles are going into the drop checker. This is the spot you want to shoot for. A section of your tank that has no micro bubbles floating around, but an adequate water flow. This area should, in theory have the lowest amount of dissolved co2 in the entire tank.
Now you might be thinking that no co2 bubbles are going into your drop checker currently. Double check to see if this is true. Look very closely and make sure there are none because even a few bubbles per minute sneaking up there over the course of 8-12 hours can drastically throw off the drop checker.
I have tested this approach after wondering why my ph and kh readings give vastly different co2 results than what my drop checker was displaying. A yellow drop checker, but only 15 ppm of theoretical co2 in the water is cause for examination and experimentation. At first I placed the drop checker in the opposite corner of the tank - furthest away from the PoO. After seeing little co2 bubbles cruise up into the drop checker I began to fool around with things.
I put the drop checker in an area of the tank were there were no bubbles, at least to the naked eye after viewing for a few minutes. I decided to let it sit there and observe the results the next day after co2 has degassed from both the aquarium and drop checker interface.
The difference in reading the next day was astonishing. The drop checker now was only dark emerald green. I took pH and kH readings and everything was exactly the same as the night before. The only change was the position of the drop checker.
Why do these bubbles throw off the reading of a drop checker?
Once the co2 gas pops on the surface of the drop checker, 100% pure co2 is ejected into the interface medium between the checker fluid - air bubble - aquarium water. The air bubble that exists between the checker fluid and aquarium water starts to have a higher concentrations of co2 than what is actually dissolved in the aquarium water. This obviously causes the checker fluid to become too acidic.
Some might argue that the co2 spray can be used just as well by the plants as totally dissolved co2. I'm not arguing that fact. The problem with bubbled co2 is that there is no real way of measuring how much there is in the tank.
If you are using a power head or diffuser, place the drop checker in an area of the tank that has no co2 bubbles at all. NOTE: oxygen bubbles from pearling may throw off results as well.
Here is my drop checker in relation to the diffuser. A bit hard to see but there are no bubbles at all in this area and my kH / pH readings align with the color the drop checker. Not only that a pH of 6.6 is obtained from the color of the checker(bromothyle blue). A pH of 6.6 and kH of 4 = 30ppm of co2 exactly.
Here's my tank after a complete rescape one week ago.