One way would be to install drain tile in the yard around the pool deck to carry excess ground water away from the pool.
I'm assuming that you have an inground vinyl lined pool. This is a chronic problem with inground vinyl lined pools, and is due to ground water being higher than the level of the water in your pool. The pressure of the ground water is greater than the pressure exerted by your pool water, and the liner floats. A half baked solution, is to wait until the ground is no longer saturated before removing water. The real solution is to provide a way for the ground water underneath your liner to be removed. This can be a passive system with a small pipe going under your liner and allowing the ground water to drain off (but this only works if you can keep all parts of that pipe below the level of the water in the pool-which depends completely on the pitch of the ground in your yard), or an active pumping system which pumps the ground water out to a drain.
get plaSTER AND COVER IT SO THHE LINER WILL NOT COMPLETELY COME OUT ADD NEW TILES OR WATEVER ITS MADE OF .
It sounds like there is a broken water line under the sand. Perhaps from a sprinker system?
Regarding pool: a liner refers to an in-ground or above ground pool that uses a Vinyl Liner to hold the water. The liner is a custom fit to the shape of the pool, in-ground pools utilizes steel, or composite walls to hold the earth back and the floor can be a thin concrete or a sand bottom.
Try using very hot water to heat the liner..
ground water
ground
the term for under water is ''ground water ''.
No the amount of weight exerted on the liner of even a litle water makes this imposible to do.
You can use bleach to clean your above ground plastic pool liner. Use one part bleach to two parts water and scrub the stain wearing rubber gloves. Make sure to rinse the bleach thoroughly from the liner before adding more water in.
The liner should not float at all. The pressure or weight of the water is what holds it down. There has to be either a leak where water is getting under or behind it or maybe ground water is forcing it up. This is sometimesa problem in the southern states where the water table is closer to the ground surface.
The only way you are going to move that liner is to take the water out that covers the sag.