I am new and I really need some guidance. I have a 4.5ft x 24ft above ground vinyl pool. When I bought my house it had a nice cover on it, but I later found out that it has sat neglected for years and they just covered it up. I wound up draining it, replacing the liner and the pump and sand filter. I fought all summer trying to get my water clear and never quite got there. This year I took my cover off and I was so excited that the water was clear with a small amount of debris on the bottom. It was ok for a couple of days and then once again green and cloudy like last summer. Over the past month i used a 25lb bucket of shock trying to get it clear. My chemical levels are always good but no clear water. The man at the pool store decided to check for nitrates and he said they were high (can't remember the #) and that I need to drain and refill. I turned the pump off for a few days and drained down to below skimmer until I had time to drain and yesterday I noticed that there was clear water with a green coating on the bottom. I put my Pool Rover in to clean it and it stirred it back to look like what it had been before I turned off the pump. Does that sound like a nitrate problem to you or more of an algae problem?