Floor drain line leak?

[stevex]

My pool water level's been dropping. We've had a very dry summer so at first I just attributed it to evaporation, but we went away for 5 days and came back to the pool being down over a foot.

I don't see a leak in the liner, and the water level has dropped below the returns. The only thing I can think of is there's a liner leak (maybe a seam) that I'm missing, or that there's a break in the line from the main drain to the skimmer.

Some questions:

How likely is it that if there's a liner leak, I'd see it? I've looked pretty closely at all the seams and nothing looks off to me. There are no bulges or bubbles or anything like that.

If the leak is in the line from the main drain to the skimmer, can I just plug both ends (the floor drain and the second hole in the skimmer, which is only attached to the main drain). I'm don't know why the floor drain is connected to the skimmer in the first place.

Draining the water out to fix it, how likely is it this is going to do some other damage to the liner? It's a pretty old pool, maybe 15 years old.

Pictures attached .. they show the progression from September 2nd through today (7 days).

Thanks

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19K gal, 16x32 in-ground vinyl, Hayward pump, sand filter, no salt, Baracuda G3 cleaner

 

[Vickery]

How about adding the critical info about your pool to your signature so we can see what you are dealing with. Where are you? What is the water table level there?

 

[stevex]

Sorry, updated the sig.

I don't know the water table level. The pool is on a hill, so about 20' from the back of the pool you're standing below where the bottom of the pool is, so I think the water table would be below the bottom of the pool. It's also right next to the house which has a walk-out basement, where floor level is also pretty close to the bottom of the pool level.

I know it looks pretty green right now but it's been in good shape all summer; the pump's been off since I started to have to add water daily just to keep it up to the skimmer and I wanted to see how low it would drop to try to help narrow down where the leak is.

Thanks

 

[pooldv]

We recommend leaving a foot of water in a vinyl pool to hold the liner in place to prevent the liner from shifting or shrinking and tearing when refilled.