Hi! We are new at this and have a 55 gallon tank w 4 GloFish, 1 zebra tetra, & 3 plattys. We have had them all for about 2 weeks and everyone has been great. Just a couple days ago, my green GloFish stopped interacting with the others and stays at one spot in the middle left of the aquarium. He kind of just twitches. He has not eaten in 2 days. Does not float upside down or sideways. Just kind of twitches and flicks to stay in the same spot. I see no changes in his color or scales. He opens and closes his mouth a lot, way more than the other fish. Should I be concerned?? Any idea what is going on? I have also noticed his eyes seem a lil bluish where the others are black.