Advice needed for new aquarium with potting soil substrate and dying fish

I find the whole thing really bizarre and if you have any advice please let
me know. There are lots of choices for substrate and there is no clear
obvious choice, so this is a tough decision for me as well when I rebuild
the tank. Many of the suggestions I see such as vermiculite and flourite
don't seem to be available here in France.

Thanks,
Michael

You can put in much less soil. Pre soak it first for 2-3 weeks also
will help.

There are a number of laterite brand names in France. Dupla etc all
make these amdenments to gravel, 2-3mm is a good size. These work well
w/o soil. You can(I would) add a bit of soil/mulm/peat to the bottom
layer with this gravel+ laterite mix. Just not as a much, maybe a
couple of handfuls per 80 liter tank.

'A bit more(2X) for a non CO2 planted tank.


Regards,
Tom Barr