Mystery leak/s

[HarbourNZ]

We have recently refinished our concrete block/ fibre glass lined pool using a chlorine rubber epoxy paint. Prior to this the pool had sat empty for at least 3 years. Pool is probably about 25 years old but in good structural condition. There were no large visible cracks and aside from some crumbling around the stairs (which we repaired using cemix). There didn’t appear to be any issues with the surface. New plumbing, pump and filter also installed. Within 24hrs of being filled and having the filter /pump going we realised we were losing water… approx 2-3 inches over a 12 hour period. The water level quickly dropped below skimmer and inlet pipes so have ruled those out as cause. A week later we are still losing water but it has slowed significantly to approx 1-3cm over a 24 hr proud. We have attempted dye tests but haven’t found any obvious leaks. We can’t see where the water is ending up ( no damp ground etc) . The pool had about a foot of water in it for about 8 days before we filled and didn’t loose any water so we are assuming the leak isn’t on the ground/ bottom edges. What are we missing here? Dye testing not helping. Would emptying and doing another layer of the epoxy be worth trying ??? What else can we try?

[Teapot1]

Have you got a light in the pool?

[Denniswiseman]

Or a main drain?

[mknmike]

I’m not going to say I was successful testing this way, but I tried using food due to test if my light was leaking.

The additional pressure and hydrostatic pressure balance of the groundwater level could have caused the main drain to not leak when the water level was low (balanced with the groundwater), but when you fill the pool, it’s pressure on the drain is significantly more, far from balanced with the groundwater.

[Denniswiseman]

Hydrostatic relief valves are designed to leak into the pool when the groundwater pressure is greater than the pool water to prevent floating. They don't need to be balanced
Your Hydrostatic relief valve could be faulty

[mknmike]

Hydrostatic relief valves are designed to leak into the pool when the groundwater pressure is greater than the pool water to prevent floating. They don't need to be balanced
Your Hydrostatic relief valve could be faulty

Right. I think the OP was thinking it can’t be the main drain or hydrostatic relief valve because the level was stable when there was only about a foot of water in the pool. But if the valve is faulty or there’s a “leak” there, it might not reveal itself until the pool is filled.

[Denniswiseman]

HarbourNZ hasn't come back since 20 November so I suspect that he's fixed it and couldn't be bothered to let us know what it was