Another local pool builder, not mine used to contract and build the pool; had a recommendation similar to that. Even if we remove the live stone up to where the water sits in the channel for the spillover area, it should reduce a lot of that loss. But my gut has been that since the beginning. I think deconstructing the spa and applying proper waterproofing and then either tile and re-stoning would see a lot of my loss go away.Gunite is like a sponge, when it is exposed to water, it will soak it up. It not a hydraulically sealed material like plaster is. So the entire stone face of the spa outer walls, with no waterproofing material applied, allows any water in contact with it to seep in. As you cycle the spillover of the spa, the water will soak into the gunite and then evaporate away or get pulled into the ground depending on water saturation. It’s also a large, rough surface with a lot of water flowing over the stones and in & around the crevices. That will enhance evaporation during hot days. So it’s not all that surprising that you’re seeing water loss.
The comments made by those people you brought out to inspect their pool sound like hedges to me - they don’t want to throw the original PB under the bus and they don’t want to be responsible for fixing his mess. It’s like they’re just shrugging their shoulders and saying, “Meh! Looks ok to me”. It’s pretty unusual to NOT waterproof a concrete wall that is exposed to water. Think about home construction with basements - you’d never build a basement without adding waterproofing layers to the outside wall that sits in contact with the ground! Same concept with a raised spa wall - if it’s going to see any water at all it either has to be plastered OR a waterproofing material has to be applied.
So I think you’re at the point where you either have to live with what you have OR spend a lot of money to deconstruct that spa and have the exterior properly engineered.
Adding an automatic fill hose, which is what my pool builder said to do... would just prolong the waste and cost.