Your specific gravity is too low. For this nem it should be between 1.024 - 1.025. Also, you are most likely running pc's and for bubble tips or bulbs you should have either T-5's or halides. Also, while I have seen the minimum tank size reflecting 10 gallons, I think they need a larger, more diverse ecosystem to truly thrive. Perhaps a 10 gallon after a year when the flora is well established......maybe.
Basically it is starving for light. It is in the process of dying. Can you take it to your lfs?