poor paradise

 My paradise fish not bright anymore. It happened so gradually I barely noticed- but then one day saw the long streamers on his unpaired fins are gone, and his color dulled. He's still just as eager to eat but often slow about it- still too busy looking up at my hand, the minnows grab food from under his nose, ha. On a very few occasions I have seem him flash against the edge of a leaf, but then when I watch close for a long period of time, I don't see him repeat it. I hate to think he's coming down with the same virus or whatever illness that my two previous paradise fishes had. Even though it was eight months without one of them in the tank, and the minnows all seem fine. Does my tank harbor a pathogen so long, or do I just keep getting paradise fishes that are generally unwell (poor breeding?) or is something about my manner of keeping them not good enough. I don't know.