Betta Fish: Me again. Something is wrong with my boy. Does anyone know what’s happening!?!? 😭

I posted yesterday and some said it looked like he injured himself on his decor. I moved him to my hospital tank where everything is soft. Today he is looking worse. Now scales on his head are missing.

5 gallons
2 sponge filters
KH 120
GH 140
PH 7.0
NO2 0
NO3 5
Ammonia 0
Temp 80

No substrate, soft silicone decor.
No tank mates
1 real plant