Didn't mean to be obtuse about special fish, just keeping the question simple. This is for otos, so heavily planted is an absolute requirement to raise fry successfully.
The substrate doesn't have to supply the acidity forever, I'm fine to supplement with peat extract as the substrate depletes of tannin.
Peat has come up in a few locations (like the link) as a suggested substrate, so I just need to figure out how to maintain plants in it.
The Barr link seems fine, but uses water column dosing. I wasn't sure if swords would prefer root feeding, that's all.