Thank you gents for your replies and sorry for my original post that is not well-organised.
1) I think you are asking how the drop checker works. You seem to think that the drop checker solution is only pH testing solution. Actually it is a precise 4 dkh solution with pH indicator added. As the KH is constant, the co2 can be relatively precisely monitored.
Thanks for your reply. But my question was whether the chemical reaction of tannis or any pH reducer substance with aquarium water is identical to what CO2 does.
2) Just like any other tool, you do not need to follow the drop checker to the "perfect light green". It is an indicator, and you can decide that your tank grows best under a blue-green, green, or even a yellow if your fish can handle it.
Its color will fade out, so you need to change the liquid frequently and moreover it will work like "an indicator" only. If this is the case, it is the time for me to put it aside too and listen to my senses.
3) I would not worry about the noise, a river/lake is pretty noisy in nature.
Some rivers/lakes are, some are not. In the nature, fishes probably would find a decent area inside the water to have a good rest and protect themselves from the possible threads while unconcious. I've just replaced the diffusers with a pair of new classic air stones. Now air particles are formed like a mist, not like air bubbles so the noise has gone.
4) Baking soda is not a very strong KH buffer, it will only provide temporary gains, I will leave reccomendations for someone with a Discus tank.
I heard this before. I also heard that phosphate-based KH buffers are more resistant. But why?
That's the first I've heard that. But then most any additive used to increase KH will only be temporary if there's a demand.
Hmmm, you have a point there. See below.
Your plants are depleting your KH because they're using it as a source of carbon.
Perhaps, phosphate will not be depleted as quick as HCO3 is so a phosphate-based KH buffer is more resistant (or stronger I must tell). Can it be?
Thanks, exv152. So a KH buffer -I am talking about NaHCO3 in fact- is actually a nutrient source as well. Yes of course it has HCO3. Sometimes connecting the dots are not easy although it happens before your eyes. In this case, this depletion is normal and even beneficial to the plants not only in terms of CO2 regulation but also as a direct nutrient. Then we must top up it everytime we felt/measured a reduction in KH of the tank water. How can we make KH measurements more practical? Isn't there a pen-like device for KH measurements in the market, just like TDS meters?
One question for you, why are you using RO water and then replenishing it with equilibrium?
I am currently resident in Bahrain and a high percentage of tap water is desalinated from the sea by large RO plants and the water is still too hard. I wanted to give a try to RO water because without doing something in person, what you hear from other people is not just enough. A second reason is that I thought Discus would not be happy with the quality of my tap water. A third one is that I like buying equipments to make me feel more miserable :-)