Peat moss does not float.
It is light, so any disturbance to the substrate will make it drift in the water and then it settles out on the bottom again.
Since peat moss is so easily available give it a try!
Pure RO in a bucket. Test to be sure it really does not have anything in it. All the hobby level test kits will show nothing. pH might test anywhere from 6-7 or so. TDS ought to be in the single digits.
Small filter, any style.
Nylon stocking of peat moss in the filter. By running the water through the peat moss you are getting the maximum results the fastest.
By using peat moss as a substrate you will get a gradual release of the organic acids into the tank.
Peat moss is a good source of the organic acids these fish need. Replicates the original source of the black water- fallen leaves etc.
Oak leaves will do the same thing- drop the pH of the water by adding organic acids.
As for what this will do to the microorganisms in the tank...
The nitrifying bacteria will not survive. They thrive in hard, alkaline water, and barely hang in there when the pH is in the 6s.
At that pH, the ammonia will all be in the form of ammonium. Still, I would use something that is NOT ion exchange to remove ammonia.
Perhaps some of the plants that specialize in that sort of water, and pretty much demand it when they are kept in tanks.