Thor isn't himself. I can't put my finger on what's wrong, exactly; he just seems really tired. Usually he's always flaring and swimming around, but now he's just lying there near the bottom. I tried to stir him up a little to see how he'd react, and he swam all right but needed to stop, like he was out of breath. Usually he's very active and healthy. He's in a divided 10 gallon, heated at 78 degrees, filtered, uncycled. The last water change was 50% today, but he was acting strangely before that.