Its a pacu, get real good at water changes. Your water doesn't look too good. Seriously start doing 20% a day for a week to get it cleaned up and then get real consistent about weekly 50%. Then go get a big tank.
Pacu don't do well singly, they stress out and freak out. When they freak out they are VERY capable of hitting the inside of that tank hard enough to break it. It needs to be housed in a group and in a LARGE tank. Due to their size putting them in a school is nearly impossible in captivity, but getting it 1 or 2 others to be with is a good start. I really don't think you can do this in a tank smaller than 300 gallons and 4-500 would be far more appropriate. You might get away with 2 of them in a 300 if the glass was thick enough. I had 2 in a 210 and I was delusional when I thought that would be enough. I now have 3 in a 450. The behavior difference when I added the 3rd one is amazing. I wish I had the room to add 3 more.