Could the substrate be getting too old (ie: compacted, depleted of
nutrients, etc.)?

Harry

Actually, I'm afraid I don't have an enriched substrate. I only have regular
gravel. Not ideal, I know, but my plants nonetheless used to do a lot better
in the past.

In any case, thank you for the suggestion. I'm sure it can benefit people
who do use special substrate, or even myself if I decide to use it. I just
might. Thanks for the idea.

Francois