You know, I agree with you on this 100%, I have a CO2 drop checker and made my own 4dkh solution but I am not really sure how accurate it is. I just added fish and I think going by their breathing rate or their trips to the surface for O2 is much more reliable, also pearling of plants.Just google drop checker. You find all kinds of info.
I have been keeping planted tanks since 78 or 79. With CO2 since 93 or 94. I can just eyeball the plants, algae and fish at this point to determine if I have enough CO2. I have found that drop checkers can only give you ball park readings and sometimes are just flat out wrong.
I have a question...what happens to the solution IF you dont change it out? Does it stay green indefinetly when it gets old? does it go back to blue? does it turn clear?
X3I can just eyeball the plants, algae and fish at this point to determine if I have enough CO2. I have found that drop checkers can only give you ball park readings and sometimes are just flat out wrong.
I just changed mine for the first time in over a year. The color still worked and indicated the level pre-change, but post change it was a lot brighter.
I'm told that because of the high lighting level in most planted tanks, the dye can sometimes be misleading.
IME guppies/endlers are a perfect fish to use for a reference point. They normally cruise at all levels of the aquarium, but if your starting to max out with CO2, guppies will gasp at the surface much sooner than any other fish. When you start seeing this start to happen, cut the bubble rate down from there. Once you see they're now back to their usual selves, cruising the whole tank. That's where you want to keep it. With respective lighting you will see much pearling from most plants, if not all.