Perplexing Swimming Pool Leak

I have a 30 year old "black bottomed" gunite pool in Hawaii that uses about 150 gallons of water daily. [I carefully measured.] Its probably done this for years but this has only become noticable now that our daily rains have ceased.
I've done the normal: plugged all inlets, outlets, used dye looking for movement, checked the tile line. I've closed the man drain and packed some A+B Epoxy around that fitting in case that was a path. I've packed the cable fitting for the underwater light with epoxy also.
Still, the level drops the same whether the pump is on or off.
For want of any other cause, that leads me to suspect the "plaster."
It is not modern "smooth" black plaster but was probably cement mixed with Hawaiian lava sand. Relatively coarse grains are visible on close inspection buy not spalling or gouges. The material extends evenly to the tile line. The plaster is intact as far as I can tell.
There is a slighly brownish discoloration [doesn't bother me] at the deepest end of the pool. Perhaps a 10 foot circle. But even there, the plaster feels intact.
Would a gunite shell leak without "real" plaster? Is it likely that this plaster is simply allowing seepage?
Thank you for any comments.
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To put the water useage in perspective I should have added: pool is freeform about 20 X 30.
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familiar with you type of construction and can inspect the pool. Some masonry is not water-tight but pools are normally constructed so as to not leak. So no one can really know the cause and solution without inspection and knowledge of that particular type of construction.
Don Young
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In case anyone else every reads this thread, I found an answer.
I was slowly feeding water into the pool through a pipe embedded in the concrete deck. At low flow rates, the water clings to the edge of the deck and a large portion was flowing under the top tile through a small gap in the grout. The water then migrated several feet to the side and found a crack in the bond beam at the level of the second tile. I knew there was a hollow "ring" at this point when tapped and removed the tile. Only later, when I saw water flow into the crack did I realise it was coming from the feed line.
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