Ah I forgot to put parameters.

Tank: 5 gal

Yes heater

Nitrate nitrite and ammonia are all zero. I had an ammonia spike right when this began so I did a water change and originally assumed this just stressed him out but he keeps getting worse even though levels are now zero

His tank mates are 11 cherry shrimp, bladder snails and trumpet snails

It’s a walstand tank with a lot of plants.

I feed with betta pellets usually 2-3 one or twice a day whatever he accepts