Few factors that came to my mind:
I was reading a comment on a FB group on how this person was giving his swords tabs twice a week (I thought to myself that’s excessive) but his plants were looking beautiful
Under fed? Maybe?
Another factor possible.
i think it is the crushed corals that is the deal breaker have you just tried to do gravel only in a cup with crushed corals removed and see if it thrives better in the same conditions rooted? Just a suggestion
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