Got a question, my pool was professionally installed and I will leave it at that. Anyway it has a sand base that was put in July 2010. It is 15X30*52" Above with a beaded liner. In the bottom of the pool it looks like little crevaces all interconnected that you can stick you finger in and dirt always finds it way to settle in. Kind of looks like a tree branch being interconnected. Now my pool was put up then the builders went to lunch and it downpoured, it filled up with about 3 " water because the liner was not in so they took it down and came back a few days later. These crevaces are in I would say a 3 ft circle about 5 foot from the walls. I am thinking it may be ground water that just compressed, I have some major any colonies outside the perimter of the pool. And I fear that. My perimiter is boxed 3 ft around the pool and filled with about 4 " stone over plastic. Another issue I had was since I had a beaded liner they did not put a full coving down so the liner 'sits', in one spot inside It feels like the liner is touching the track at the bottom. I had the builder out and he said drain it and he would fix it or wait til you need a liner and he dug with his hand outside and said see the liner is not pushing under the track. So I left it. I am just a perfectionist and have a hard time when I see things not always done at a high level though acceptable.