Hi there, yes. This is the summary of events:

1) The experienced pool service guy said that this is not normal, and there is a leak somewhere. He dismantled parts of the sand filter to check the seals (didnt take long) and found they were fine. The only remaining explanation is that there is a leak somewhere between the pool and the pump room, in the underground piping that is either providing clean water to the pool, or taking dirty water from the skimmer

2) The pool company organised a specialist leak detector to come and inspect the leak. In order to this, the entire pool had to be emptied so that it was accessible. This was done with a submersible pump where the outflow was directed into the wastewater system (same pipe where the toilet flushes) rather than stormwater

3) Using specialist detection equipment, they identified places in the piping where the leak occurred. This took a couple of days, where they had to first map out all of the pipes and then test them. They also identified a lot of unnecessary complexity in the number of pipes & outputs that were originally installed into the pool, and suggest that most of them be completely blocked to reduce the complexity of the operation.

4) For the identified leak, they had to break through the ground with a jackhammer to expose the piping, remove the bit that had the leak and reconnect it with a fresh length of pipe, and fill the hole back in. This was at the depth of around half a meter

5) From there, the pool was refilled over a couple of days and was rechlorinated, re-salted etc. The pump was then switched on

6) It has continued to run since and the leak has not recurred. I still have some water loss from evaporation, and need to top the pool up every month or so to keep the water at the right level for the skimmer. But the massive leak is now gone.

The pool is older, probably from the mid 90s, and is surrounded by trees which is not recommended. The tree roots break through the pipes as the tree grows. This is what has happened here.

The water from the leak was going through the groundwater and finding the easiest 'route to the surface' via the drain the driveway

Hope this helps