I drained my pool a few inches below the tiles and closed the pool with a mostly solid cover with a mesh opening in the middle. I have had a pump under the cover to keep the water level from getting to high. I peeked under the cover this weekend and noticed a bath tub line around the pool. I am hoping it is just dirt and once I open the pool a few days of SLAM will eliminate it. My pool was replastered this past July so I am very nervous. I closed they same way I have in the past but never had this ring before. Unless I just didn't notice it because the old plaster was so worn. Any input/suggestions on whether I should be concerned or what I should do?