This has been going on for a couple of months, but other than sitting - on an ornament, on a plant, or on the bottom, one of my blue gouramis just sits most of the time. I put him in quarantine for a month and he swam a bit more, but didn't appear sick so I put him back in general population. He goes to the top for air and food, swims a bit now and then, but otherwise just sits. The others do not molest him and no one else is acting strangely. Any idea what's up?