Finding/fixing a pond leak
I've had a koi pond leak for over ten years and have expended no end of money and effort in finding and fixing it. It's a small leak but adds about 50% to my water bill.
My pond is gunite/plaster and shares a common wall with my swimming pool. Fortunately, the water level of the pool is about 16" lower than that of the pond, otherwise the chlorine would have leached into my pond, killing my koi.
The common wall section which leaks is only about seven feet long but it's thick and the upper two feet are comprised on mortared granite boulders, not plaster. That, apparently, is the section that's leaking.
if you wanna find a leak in a thin-walled wading pool, you just wait until the water level stops dropping and then you know that the leak is somewhere at the water line. But with my thick walls, the leak could be at or below the water line on the pond-side, since hydraulic pressure could force the water to flow UP.
I've tried draining the pond and coating the granite wall with water sealant and using pool putty (which hardens underwater) to thoroughly coat the grout joints. I even bought some day-glow green leak detector fluid which allows you to trace where water is being sucked through the wall (didn't work because the leak isn't big enough and the lighting is bad).
If the high water bills weren't enough, this leak is also fostering algae growth in my pool, requiring me to clean the filter monthly Any recommendations on a fix, regardless how looney, would be GREATLY appreciated. I'm at my wits end!