I disagree about the KH standard. If your KH test kit is good, making your own by trial and error is an adequate way to get the 4 dKH water. Just be sure that you use distilled or deionized water. Any error in the KH of that water results in an equal error in the ppm of CO2. This is not a problem if you get within 10-20% of the right KH. After all, the best a drop checker can do is get you to within about 20 to 40 ppm of CO2, because very small errors in reading the color of the drop checker make a big difference in the CO2 ppm.
All we are doing with a drop checker is working around the problem that so many of us had using the pH/KH/CO2 chart to measure CO2 - that was where those measurements indicated that we had 100-150 ppm of CO2, but we still had bad BBA and no gasping fish, indicating that our actual ppm was closer to 10 than 100. Precision in measuring CO2 ppm just isn't available for less than $1000 or more.
Ok then the above makes perfect sense. But I'm not making my suggestion due to his KH test but based on the fact his color changes from blue to yellow in 20min and the rapid change from yellow to blue? Unless he has Co2 blowing in directly into his DC which would explain the rapid color change to yellow, but I did not get that based on his description. How would you explain the change from yellow to blue in 5 min? Maybe his Bromothymol Blue is Bro something else?
I have been using DC's for a while and my experience under Mazzei injection has never yielded such rapid results and my PH pulldown is very efficient. My change from greenish yellow to blue also does not have such rapid a change either.
How Many drop of Bromothymol Blue do you add to your DC and When was the last time you changed it?
I made my own 4KH water. I don't care that much about getting exact results - just so I can see if it's going up or down. The bba tells me if it's going TOO low....which consistently happens when I get to the darker green/blue green area. So I think my homemade preparation is fairly close. My plants tell me which color I want my drop checker...when it's greenish yellow, they grow like mad. That's all I care about. Good to change out your solution once in a while though, if in doubt.
Why you let your Co2 drop to levels to allow BBA to grow or have varying Co2 ranges depending on what plant growth you want is a little perplexing to me But you have more experience than ccLans with using Co2 and therefore have a better sense of whats going on with your Co2. He cannot afford to settle IMO in his early stages with Co2 so he needs to get it as accurate as he can at this point.
I haven't changed mine, though, in months, and it's still working just as when I first put it in.
I 100%disagree with you on this because it will have an impact on transition time. DC's should be refreshed a max of 3 weeks if one is after fairly accurate range.
I put carbon in my filter a few months back. I have no idea if it was coincidence or not, or what happened, but within days my hygrophila polysperma, which I haven't been able to kill for over a year of experimentation and messing around with co2, lights, ferts, etc., suddenly started developing strange new growth, it looks like parts of the leaves were actually chewed off (but they weren't). After a week or two, can't remember exactly, I put together that I added the carbon right around when this started. So I removed it. Since then, doing lots of ferts and upping co2, it's just now starting to come around and grow normally again. Coincidence, possibly, but I won't be attempting carbon again anytime soon
Well I have never had a issue with using Matrix Carbon which I' have been using for months and I use about 14oz. Per Seachem Matrix Carbon is not like the regular carbon, so if this were the case then I would have to say I would experince this as well and I do not.
I also have to add Ca/Mg to RO/DI water but like I said I do not experience such issues. Based on my experience with plant health/growth I would recommend Carbon, Matrix or other.... highly.