i think..no offense that you and yoru family need to research more. i mean its just not fair to the fish...no hiding spots..nothing.. its just not a good situation...maybe try some rasboras or gouramis?
Fin nips are common in juvenile piranha such as these. (I hope they are juvenile by the shape unless they are malnourished!)
All my piranha tanks have no hiding spaces or plants. Just lots of good quality water and flow! Tank decor is down to personal taste imo.
Lovely little cariba. The water does look cloudy though!
Very nice piranha i dont mean to sound offensive but smarten up the tank, add a back ground, do a waterchange and increase filteration and get a bigger tank.