Greg at SeaChem is letting me use some of their new Black flourite.
Like the normal stuff, it's leach free.
ADA is about the only thing that leaches nutrients or soil based sediments or Jobes sticks etc etc. Onyx some KH/GH, but it's CaCO3, calcite, so that's to be expected to some degree.

What is the water change routine as it stands?
Most Discus w/c routines work very well with plain old EI dosing, which was worked out originally on a 90 gal with 6 Full sized Discus+ other cories, ottos etc. I just did 1x a week 50-60%, you can do 2x 30% etc, or 2x 50%.

The issue is not the sediment, the issue is all the NH4 from the food, that is why you do the water changes(not really to reduce the PO4 which is not a toxicant even at very high levels,, and NO3 needs to be very high also), adding plants reduces NH4 via direct uptake and adds O2.


Regards,
Tom Barr