Image by Alexas_Fotos from Pixabay
Tools
Speciation diagram
of CO2/HCO3−/CO32−as a function of pH
Created by Gábor Turu
Some plant species seem to need a slightly acidic pH (pH < 6) to growth well under some conditions (see picture below).
Suppose your aquarium water has a KH of 1 (similar to
Tom Barr,
Gregg Zydeck, or
Joe Harvey to name a few).
Find out how much CO2 would you need to add to your aquarium to bring the pH down below 6. Hint: Enormous!
PS: Tom Barr's pH is 5.6 [when CO2 injection is on], and Gregg Zydeck's is said to be as low as 5.4
(see 2hraquarist.com).
So now you can probably guess why it is "necessary" to add such a huge amount of CO2 to the aquarium if you want to meet the pH needs of some acid-loving plants.
Yet the best way to achieve the desired pH is not to add excessive amounts of CO2 to the water, but to remove bicarbonate from it.
With 0.1°dKH you only need to add 10 ppm CO2 to the water to achieve the same pH as Tom Barr with 1°dKH and 88 ppm CO2!
And yet your plants will grow just as well in this aquarium as in his.
