Help in locating a leak

[bbutters]

I have a bit of a leak and wanted to see if anyone has any bright ideas I haven't considered.
Water level continues to drop to about an inch up the mouth of the skimmer. It stabilizes there - I've closed the suction to the skimmer and stopped topping off the water, only drawing from the main drain which appears to be a dedicated pipe (only one open pipe at the bottom of the skimmer). So I consulted the leak checking posts here on TFP.

With the skimmer suction closed and the skimmer drain plugged, the water still dropped down.
With each of the two returns closed and plugged, one at a time, the water still dropped.
I can't plug the drain but I feel pretty sure that the leak can't be in the plumbing - my equipment pad is such that virtually all of it is below the waterline, certainly all of the buried pipes, and there are no obvious gushers around the equipment.

So I got a dye check kit and double checked around the returns, nothing there, and around the skimmer - found a fairly evident leak on one side of the interior of the pool-side faceplate. Gasket must be failing. I got some pool putty to see if I could temporarily solve and verify this and while the dye no longer shows evidence of a leak there, or anywhere around the mouth of the skimmer, I'm still seeing the water level drop (albeit perhaps a bit slower) to the same spot.

Only thing that concerns me is that the concrete around the skimmer is pretty well heaved and that surely isn't helping things. But I just can't detect a leak - just user error with the dye? It would be tricky to check around the base of the weir but I don't think there is a flange that far into the skimmer...

Will a pro resort to dye checks if the plumbing doesn't show signs of leaking?


Other strategies

 

[AQUA~HOLICS]

This is the company I use.

 

[bbutters]

With the skimmer suction closed and the skimmer drain plugged, the water still dropped down.

Hm.
I haven't been using the pool the last few weeks, it's set to be closed end of the month, so I shut the skimmer suction off and haven't bothered keeping the water level up.
Result is that after a week or so, the water level stops dropping at the skimmer mouth, and when I look inside the skimmer what I find is that it's empty/dry, but I can see water several inches down in the suction pipe.
So in the above scenario, maybe I was leaking at the skimmer flange, and now with that repaired I've isolated to just some kind of pipe leak.

Seems at this point my only recourse will be to demo the section of deck that houses the skimmer - the concrete is heaved and cracking around the skimmer anyway - and locate/repair the leak in the pipe. Ugh.