Sinking Angel fish

[Mrs Smith]

I bought a tank and fish on Sunday and one Angel fish is sinking to the bottom. He can swim to the top and does eat but then sinks. Apparently he has been like this since December. He is also slightly curved, not sure if this is relevant.
Thanks in advance

 

[Aiken Drum]

Please take a read through the "unhealthy sticky" and provide as much detail as you are able.

https://www.aquariumadvice.com/forums/f17/before-posting-about-unhealthy-fish-read-this-32451.html