Hi,
I’m a US fish keeper and first time poster here. I keep a handful of blackwater species, and here’s how I prepare my water. I use a Brute 32 gallon trashcan (it sits on coasters so I can movie it around the fishroom), toss in a couple large filter media bags full of Sera Superpeat granules (Fluval peat didn’t seem to get the pH as low as Sera) and reconstitute the water a small bit with Kent RO Right up to about 60 ppm TDS. The pH in the trashcan after a few days is around 5.2. I keep 1 to 2 small filter media bags of peat in the blackwater tanks themselves. When I do weekly water changes, I check the tanks and the pH has continued to drop to around 4.5 or so. This method would work well with a 5 gallon bucket or any other size container as well.
Steve