Hi all, In terms of water softening think you can make your own "active substrate". I've never tried it but I'm pretty sure you can, and this is how.
Active substrates can lower pH, because they have a high CEC and the initial exchange sites are filled with a proton (H+ ion), this is described as having a "low base percent saturation". Ion exchange means that H+ ions are swapped for other cations, including the basic cations Ca++, K+, Mg++ etc with exchange occurring dependent upon the relative abundance of ions and place on the lyotropic series - <
Cation Exchange Capacity in Soils, Simplified>. We use pH as a proxy for acidity and alkalinity, and it is the ratio of H+:OH- ions. Add H+ ions and pH falls, another way to think of this is that acids are "proton donors", and bases "proton acceptors".
Clay minerals from areas of high rain-fall with acid soils naturally have all their CE sites filled with H+ ions, because all the other ions have been exchanged for H+ ions (from the rain-water), this is the "Akadama" or laterite scenario, where only the very tightly bound Al+++ and Fe+++ ions are left. The same applies to sphagnum peat, which also has CEC, all the exchange sites are filled with protons, in this case because sphagnum peat only forms in rain fed mires..
So to make your own active substrate that combines a low base percent saturation with a high CEC, you can take a substance like Tesco's moler based clay cat litter, and leave it out in the rain for several months and the exchange sites will have all the basic cations replaced by H+ ions.You could add sphagnum peat if you wish.
You might be able to speed the process up by using a stronger acid than rain water (really dilute carbonic acid H2O +CO2 ~ H
2CO
3), but you would have to take the anion into account, meaning that either acetic acid (CH
3COOH) in solution as "white vinegar" or a solution of citric acid (
C6H8O7) might be better than hydrochloric acid HCl (H+ Cl-), although you wouldn't need very much HCl.
cheers Darrel