I have a brand new above ground pool. It has a sand base. About 3 days after it was installed my wife and kids got in and left a few divets and said the floor was mushy. What's going on? Also, how do I clean my DE filter? It's a waterway Clearwater 2 from namco. I understand it needs taken apart but how is this done? Once I take care of this, I'll start my chemical questions. Thanks.