I suppose you could make some liquid rock!
Since these materials remove the KH, you could make some high KH water to soak the substrate in, see if it would reduce the problems with KH being removed later, when things are set up.
I suppose you could also add fertilizers. With a high cationic exchange capacity you could pre-load the substrate.
STS in the 88 gallon tank is still looking good, the water is a lot clearer. (I am running 2 canister filters on it).