Betta Fish: Fins nippin

Hi guys! Can someone help me please what could be te cause of fin nipping? Is it just long finns or something else? 😕

Most of the time his fins are closed (second photo).

Informations:
– He is in a 5 gallon tank along with neocaridina mates.
– I clean and change half/third of water every week.
– Light is set on clock 12/12 hours.
– Filter in sponge with slow flow.
– The heater is set on 76*F.
– There are only natural plants.
– The landscape is made out of aquarium expanding foam without any sharp edges.
– i feed him once a day with fasting at the weekend