I have rescaped with ADA Malaya AS six weeks ago. My reminaralised RO has a kh of 6 but the tank water is currently zero.
I am not sure as to how long this will continue or the benefits but as a low kh requires very little in the way of additional CO2 I have had to turn the BPS of my CO2 down to stay in the lime green zone and is quite easy to drift into the yellow if I did not have a computer to control the dose.
Are you experiencing the same effect?
I was warned that this would happen together with the nh3.
I have got Malaya in my tank from about 6 months, and tap water hardness 2dKH and 6dGH, and substrate is still driving hardness in the tank to 0dKH and 2dGH.
Anyway, this is because of cation exchange capacity (CEC) properties of the substrate, which is catching cations from the salts disolved in water and giving back hydrogen ion and this process is producing acids lowering pH, and softenning the water which is messure of disoved Mg and Ca cations.
After some time substrate will be full of cations and this process will end. Bigger the water hardness, than sooner this will happen. Finally KH will stabilaze in the tank at the same hardness level as hardness of water poured to the tank