Identify dying plant

[BrushYrTeeth]

Hi! I posted a fews ago about my plants. Since then ive gotten a new light and all of my plants are doing alot better. Except this one. If anyone knows what it is, that would help alot!
i have proper lighting and fert and im lost at what to do.
Any advice for what to do or what type of plant this is would be greatly appriciated.

Ps, the water is blue from a fungus medicine for my betta.

 

[Autumnsky]

Check Bacopa Caroliniana
Bacopa monnieri aka Moneywort

 

[NicosAquatics]

Small leaf bacopa.

Super hardy plant. Surprised to see this.