Water behind vinyl liner

Last year was our 2nd year with a 18'x36' in ground vinyl liner pool. During the summer when heavy rains occurred there would be water behind the liner and after a few weeks of no rain it would go away. After I closed the pool for the winter we received heavy rains which I though filled my pool because the cover had water on it. I removed a corner of the cover and saw that the wall had bulged out with water behind them, we removed the water from behind but it continued to rain ( not heavy ). When I removed the same corner this spring there was water again but not nearly as bad, I removed roughly 500 gallon from behind the liner. From my understanding there is no drain tile around the pool. ( Steel walls ) I also have a considerable amount concrete around the pool. My question is this: Could all of that water be left over from fall and from the thaw of spring? Could this be surface water finding its way to the outside of the pool? The back yard is ALL clay with sod on top. I plan on putting drain tile around the perimeter of the pool roughly 3' deep or until I hit clay. I have also considered adding a Hydrostatic Relief Valve to my main drains. Has anyone ever had to deal with this before? The first year we closed the pool the rain wasn't nearly as bad and we did not have this problem. Any suggestions would be fantastic and welcomed.

The problem of 'liner float' results from ground water levels that are HIGHER than pool water levels.

Hydrostatic valves are utterly useless with vinyl or fiberglass pools. They depend, for function, on water under the pool reaching a higher pressure than water in the pool -- but for this to happen, you have to have a heavy pool -- concrete!
On liner pools, the liner bulges long before there's sufficient pressure difference to open the check valve on a hydrostatic valve!

You have two options:

1. During wet times, raise the water level in the pool to the overflow point, OR

2. Install a 'french drain' in the ground around the pool, with the drain piping at least 2' below the normal water level of the pool. Drain this piping into a 'sump'. An old 30' gallon poly barrel would be perfect. Place a automatic sump pump in the barrel, and run discharge piping to some point downhill from the pool.

Right now? You should raise the water level in your pool. Try to gently work the liner back into place, as the water level rises. Hopefully, you'll avoid liner wrinkles.

Good luck!

Thank you for the response.

We are moving foward with the tile around the pool and hopefully this will eliminate or at least minimize the issue. If this does not help we also have discussed installing a single pvc pipe about 8'-9' down as close to the wall as possible and covering it with a landscaping cover and just bilge the water out form there when needed. Again we appreciate the feedback as it make us a little more comfortable spending the $$ because it re-enforces what others have told us.

Hope it all works out for you!