Last week, the pool was drained, prepped, and new liner installed. Vacuum fan ran for 24 hours while filling the pool. All good. Then massive rains came and this morning there is water under the liner. It's not what I would call major, but clearly evident at floor and wall intersections where it is spongy. The whole liner seemed to be sort of bowl shaped in the deep end before the vacuum and water weight formed it to the walls and floor (Is this normal?), and now the tight form has gone back to more of a curved shape where there is water under it. I guess the liner is a tight (stretched) fit, and maybe that's why it's not wrinkled at this point.
At this point the steps have been cut in, but nothing else like returns or skimmers. I've been here 3 years and the first 2 years it never floated. This past year it did, but I had a 6 ft. long rip in the liner that when rain water got above that it seemed to cause it to float. But we have also had tremendous amount of rain in last several months.
When the liner was out, the contractor recommended a "behind liner drain", basically a 3/4" pipe running from a point near where the deep end vertical wall and slope intersect, to a spot on a down slope in my yard about 2 ft. below the normal water level. I elected not to do this as I had only had problems when the liner was ripped, but now that I seem to be having problems still, I plan on going ahead with it. I know the drainage in the pool area needs to be worked on either with french drain or maybe underground drain off the gutter. The pool is built on a slight slope so grade on one side (about 10 ft. away) is above the water level, and that's where the gutter is. This "behind liner drain" won't stop the ground water, but is supposed to relieve what ever get in there. I can't find any information anywhere about this device and would like to know other's experience or recommendation. If water is coming in from shallow end area, will it migrate all around the pool walls and then through this 3/4" pipe with a grate on it? I guess it's similar to a well point but it's not under the entire pool, and is designed for gravity flow. Any pool builders out there?