Prazi will not work for internal parasites, but works great for flukes.
I had a fish that was suffering from flukes, and it looked a lot like yours, a pinched back and cloudy eyes, and eating a lot. Then it started getting skinner and got discolored spots on its sides and the fins started rotting away. I did a FW dip(2 min) and over 10 flukes came off my 2" wrasse. By the time I caught this fish it only lasted a few days in the QT. The disease was too far along.
IMO start treating ASAP with prazi. Good care, proper nutrition, and a properly functioning immunity system is not enough to fend off flukes, it requires medication. Good Luck.