Search for mysterious leak leads to solution

Nothing can be more frustrating to a pool owner than having a beautiful pool that loses water, chlorine, salt and Cyanuric Acid. Now, most people know a pool must have chlorine to keep it clear and prevent algae and other biologics from growing in the water, but few know what a salt water pool does and even less people have heard about Cyanuric Acid.
When my pool’s Jacuzzi began to lose water, I was really frustrated. I had spent quite a bit on the best plaster at the time (Sunstone, Black Pearl) and the plumber had pressure checked all the plumbing. My greatest fear was that my pool was leaking from somewhere underground, or in the Gunite shell itself.
That would have been bad. Most new pools have auto fills so if you have a raised Jacuzzi above the pool the pool itself will continue to stay full. This was the case with mine and yet my Jacuzzi was halfway empty in the mornings until the circulation pump filled it from the pool and it began to spill over again.
As a result, my chlorine and salt were being depleted and diffused by the auto fill trying to make up the difference for the lost water. I knew there was a leak somewhere, but I didn’t know where or why. I called in Ken Howard, a pool builder friend of mine, and we tried the bucket test.
The bucket test is where you place a bucket on the top step of the stairs in the pool and fill it with pool water to match the level of the water in the pool. The theory here is that the evaporation rate of the water in the bucket will match the evaporation rate in the pool. With the auto fill turned off, a leak in the pool would become evident from a much faster drop in the pool water than in the bucket.
From our observations, there looked to be no leak in the pool itself, but it was difficult to be sure. Could the leak be in the plumbing? We then proceeded to Step Two and plugged all the inlets, jets, drains in the bottom of the pool and skimmers.
I then dove into the pool and the Jacuzzi with scuba and a weight belt (man, was the water cold). I took with me a small syringe full of purple dye. When you are near a leak under water and you squirt some dye into it, it will flow away and disappear into the opening as if being sucked away by a vacuum. I squirted dye at all the penetrations of the plaster but still no luck. The plaster was not leaking around the piping.
By this time, I was totally stumped. No leak in the pool, no leaks around the pipe penetrations or skimmers and the Jacuzzi was still low every morning before the pump turned on to cycle water through the filters and into the spillways from the Jacuzzi.
I turned off the power to the pool pumps and shut off the auto fill valve. Sure enough, the Jacuzzi water level dropped and dropped. By the second day, it was hovering just below the seat top in the lower well of the Jacuzzi.
By the third day, as the plaster began to dry out, the water level was relatively unchanged, but you could see a long wet uneven line in the plaster about two inches down from the seat top that ran parallel with the seat almost all the way around the Jacuzzi. There was the crack! What a weird place for the plaster to separate I thought. Why would it do that?
As it turns out, Gunite, when shot in a large pool, creates re-bound or dry non-sticking material that must be shoveled out of the pool and discarded. Here the Gunite contractor shoveled it up and used it to build the tops of my benches in the Jacuzzi where it eventually separated and cracked the plaster.
The moral of the story here is, use shot-crete — a mixture of concrete and gravel to build your pool shell. You always get what you pay for.

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