I need advise as to what is going on with this tank. About a week ago I shuffled my fish around so I could move the fish out of the tank that is having the ammonia problem. The ammonia is 2.0, nitrite is 0 and nitrate is 5.0. I have a four stage exterior 525gph filter and I had a hang on, which I have moved that one to the tank that I moved the fish to so it could help with the load. I have had perfect readings in this tank since I set it up over a year ago. I removed the 200ml Phosguard bag that I put in there to kill the algea. I even did a over a 50% water change after the fish were removed. Can anyone help me, please?