Help i have a serpae tetra with a popped out cloudy eye my ammonia is at 0 nitrite is at .3 ph is 7.5 GH is 17 ( I live in an area with very hard water but have had the tank running for 8 months ) KH is 7 we have also had a number of fish disappear and a green tiger barb with the same eye problem and died. The tetra is in the hospital for now... we do weekly 20% water changes once a week on a 110 g tank. Should we treat the tank with antibiotics?