I had AG pool installed April 6. I have 5-6 big indentations under floor of liner. They are about 3 inches deep and look like sink holes. Liner is so sucked down around them, you can't get any of the sand to move... However, walking in some areas of the pool, it feels like you can feel sand shifting around (how can that be with weight of water?). We have crawdads big time, and installer said that might be a prob, but thought it wouldn't be bad since pool was going to be buried 18 inches... Wrong about that! I hope liner holds up. Have to be careful when vacuuming. Read some old threads on using portland cement and other ideas, but I am not gonna mess with draining pool and when I just got it set up. Maybe in a year or 2. 


