New liner leaking

[Poconos]

Being an inground the water could be sneaking underground and you'll never see it. The fact that the leak rate has slowed or stopped tells you about where the leak is. At 8" down I'm assuming it's below the skimmer so that leaves the return pipes or the liner-stair interface. At 4 GPM leak rate a dye test should find it easily. I found one at the deep end with a rate of about 3 quarts per minute. I have suggested in past posts to use a dye made from dye markers available at dive shops or just plain beet juice. Chopped up raw beets from the supermarket boiled in water. For the squirter you can use a small garden sprayer with a long piece of auto vacuum hose attacked to the nozzle somehow. Silicone seal, tape, or whatever works. Tape the hose to a long piece of 1/2" PVC pipe and you have a long wand to squirt anywhere. Position the hose near where you want to check, let the turbulence settle out, and give a little squirt. When I got within 6" or so of my leak it was obvious. Three small slits in the liner where the bottom blends into the sides. Patching was another topic.
Hope this helps.
Al
Edit: Also, to rule out the return plumbing just plug the returns.
Also, if you think patching may be in order get yourself some Boxer-100 adhesive. It's a slow setting type that won't curl a vinyl patch and makes placing it easier.

(ajs-1 leak detection)
In case anyone wonders what this is, it's a unique thing I can search for to find this post again.