But, how is it that the pH is naturally fixed between 6 and 7 with aquasoil ? Is it the natural balance between KH (=0) and dissolved CO2 that determines that pH value ?
Hi Cedric,
To understand my answer to this question an understanding of what "pH" actually is will be required. Many hobbyists worry about pH at the wrong times and this causes more problems than if they did not worry about it. Have a look at this post, which attempts a simplified explanation of pH:=>
Unlimited nutrients using E.I.
If you are able get a better understanding of pH from that post you might now be able to understand that when other ions are added to the water, such as carbonate (CO3) or bicarbonate (HCO3), which have a negative charge, it is easier to understand that these negative charges will attract and hold (thereby neutralizing) some positively charged (H+) Hydrogen ions. The effect therefore is that neutralized
positive charges of the captured H+ are
effectively removed from the water and are removed from the calculation of pH, which is a calculation of the ratio of free floating (OH-) to (H+).
This is what the term "buffering" means. Any agent or procedure that neutralizes a quantity of the H+ and therefore increases the pH.
KH is a quantitative measure of the number of available negatively charged particles that have the ability to neutralize H+.
Clays soils typically have a high CEC and these clay particles have the ability to capture and hold certain ions, including H+.
When new Aquasoil is submerged it will capture and hold the acidic H+, thereby giving it the reputation of "buffering", however, the particles can only capture and hold a certain number of positively charged particles. After that limit is reached any more acid that is released into the water will simply accumulate and the "buffering" ability of the sediment will vanish.
This claim of "..pH is naturally fixed between 6 and 7 with aquasoil..." is taken out out of context and used as advertising because, as explained, this is only a temporary effect.
If you understand these concepts then you will see that there is no such thing as "natural balance between KH (=0) and dissolved CO2"
Any CO2 added to the water having no buffering capacity (KH=0) will cause the water to become acidic simply as a result of the Carbonic acid phenomenon. If CO2 is added to a tank that has both zero KH as well as having new Aquasoil, then the Aquasoil will absorb some of the H+ produced by the CO2 interaction with water, however, as CO2 is continued to be injected, the buffering will be overcome by the continued amount of H+ being produced. Any buffering agent can be overcome by adding enough acid.
There is no magical pH 6 to 7 buffering. The advertisement may simply assume that the hobbyist's water has some level of natural pH and KH that already falls within this range and that the additional initial buffering of the clay (temporarily) is enough to maintain the pH within this range regardless of any additional injected CO2.
Hope this clarifies.
CHeers,
