1) By binding carbonates/bicarbonates and releasing of humic acids
2) Yes, if your KH is low to begin with, it will lower KH to undetectable levels until substrate is finally exhausted
With regards to 1). If it binds carbonates/bicarbonates, how about in the situation with ro/di water with 0KH?
If ro/di water is pH 7 and it has no KH for the soil to absorb, then the drop in pH is accounted for just by the release of humic acids by the soil?
Assuming I use my tap water. And the soil lowers KH to 0. If i replenish some KH with KH booster so I can keep some shrimp which like a bit of KH, the soil will also then reduce the added KH to 0 as well eventually? Hence the necessity to add KH regularly. Is this correct?
Well according to many shrimp keeping resources, neocaridinas prefer a little carbonate in their water to achieve their ideal breeding parameters. However, I have seen reports of people keeping them in caridina parameters as well. I'm not sure what their fry survival rate is like, but it has been done. Not many breeders are going to keep neos in buffering substrate, though. It's just not necessary and it's expensive. Neos, as well as 99% of plants will thrive in inert substrates. I personally can't justify using any buffering substrates for anything other than caridina shrimp. I also don't mind dosing the water column with ferts from day one either, so it just depends on your goals there. If you want hands off feeding for the first 6 months to a year, then maybe ADA will suit you better. That's the only advantage I see for using this substrate for plants. Eventually you will need to buy ferts, unless you re-scape the same tank every time the substrate stops providing for the plants.
Thanks for the advice! I am very open to the option of caridina shrimp. I have a few of them in my small 5g planted tank and they are doing quite well. They've not started breeding yet; only had them in a few weeks and maybe they're not comfortable in the (suboptimal) water parameters I have in that tank.
I do have a decent selection of ferts, both from the seachem range and nilocg (ei dosing bottles, fe, thrive+ and thriveS).
Wanted to try aquasoil after watching all the ADA videos on YouTube. My other choice was Tropica soil.