very sick fish

Question
Hello...I have a cichlid/parrot fish that has been sick for the past month.  I've had this fish for over a year and he has always been healthy and aggressive until one day it began swimming funny and not eating.  The fish ended up behind the filter motionless except for its breathing.  I thought surely it would die and was sad because he is my favorite fish.  However, as I waited for his death to come naturally...well, it never did.  It has now been a month and the fish just stays behind the filter only moving if i tap the glass or occasionally to eat.I hate to see my fish suffering but have no idea what to do.  He appears to have lost some color and weight, and his gills might be slightly red.  The only thing  that I can remember doing differently before his onset of symptoms is a complete water change. But the other fish are fine.  I will be very grateful for any advice that you could give me. Thankyou.  

Answer
Hi

Parrot fish is not always health as it looks , they always have this swimming bladder problems , on the other hand I suspect that it is the case , it looks to have some internal problem , you can use antibiotics to treat that , also try to use anti septic for the red gills , add some salt to the water , and try to get tasty food near its mouth to eat , that might help