Help! My comet goldfish isn't swimming! It's floating next to a plant but not sinking to the bottom floor either! It's right side up so it's not floating upside down. I researched a bit, and it could be that the water is lacking oxygen? I'm not sure! Help, it has been floating there since yesterday... Should I change the water? I don't think it's being overfed because I only feed it once a day. It has never gulped for air at the top before either. It just started to not swim.. and I'm worried!