jayne marsden

Hi I am new to this site and need help urgently.I have a forty year old gourami who has never been ill ( i've had him 24 years ).About six weeks ago he started to go off his food so I tried him with different types of food thinking he was probably bored with what he was eating.Not actually realising there was something wrong.The other week I noticed he had slight red on his fins but not any more.He has stayed at the end of the tank,lethargic,looks dark and yesterday he passed a little bit of pale green faeces.All water checks are spot on.I started treating him on Friday with anti-bacterial treatment.I have treated him again today and he is responding slightly now but is still not eating.Can anyone please suggest anything.Any help would be appreciated.Thankyou