If, like Roger, your GH and KH are very low, peat, or the addition of leaf litter, can really have positive effects.
If like mine, your water GH and KH resist changes, that's another matter.
At one point, as an experiment, I added almost a bushel of almond leaves, to my 300 gal system, almost totally covering the subsrate,
yet the pH and alkalinity barely budged.
Even though the hard water in my tank turned the color of strong tea, the pH dropped from 8.2 to orly 8.

I also use lots of driftwood, that would supposedly alter water parameters, but if alkalinity is high enough, that water with fight tooth and nail to resist any and all suggestion of change.

This is where an RO unit become crucial, coming in handy, for many fish keepers that want species like Altum angels, Uarau fernadenseepezi or Heros liberifer, from low mineral content rivers such as the Rio Negro of Orinoco.
For me, with such high hardness, and high alkalinity, an RO unit would seem too wasteful, so I opt for species that are already adapted to liquid rock.

I sometimes amazes me that cetain rivers where I collect in Panama, look like they should be low pH, and soft water, but yet test out to be quite the opposite.
