Diamond black is the stuff.
Add roughly 1" or peat or add 3/4" of DB leonardite.
You can add a dusting of peat into the leonardite + mulm.
Then cap that with flourite/onyx sand etc.


This will allow you to uproot plants and move them without a mess as well as re slope any terracing and prevent "flat tank syndrome".

Regards,
Tom Barr