Lost a foot of water overnight. Trying to figure out how.

My wife and I had a new home built last summer/fall. Our new pool went in towards the end of the construction period. FT Kelley, the premier installer in our area installed the pool. I believe it is a Cardinal kit and the equipment is all Hayward. The pool is a standard 18' x 36' with a 3' shallow end and an 8' deep end with a diving board and a slide. The equipment consists of a 1hp 2600 series Super Pump, an S210S sand filter, a 250k btu Universal H-series heater and an Aqua-Rite Chlorine Generator.

Unfortunately, because of weather, the pool had to sit for at least a month with no cover before the concrete decking was poured and cover anchors and cover were installed. Some concrete from the pouring process made it into the pool, as well as a decent layer of fine, wind-blown dirt/silt that completely covers the bottom of the pool. I have just started what I feel is going to be at least a two-week process of manual vacuuming to clean it out. I started yesterday, then went to work last night. I came in this morning to find we'd lost at least a foot of water from our pool. I think I know what happened, and, if I'm right, I did it to myself. I want to run this by the other users here to see if what I think happened is feasible.

I've attached a rough drawing to help explain my theory.

As I said, I was vacuuming before work, and when I left, I turned the pump off, but left the multi-port valve in Waste. I also left the skimmer pole with the manual vacuum attachment sitting in the shallow end of the pool, leaning against the side so I wouldn't get air in the hose and risk having to prime the pump. Pretty dumb idea in hindsight. Anyway, the waste line runs down to a storm drain in the back lower corner of our property, outside of our privacy fence. The waste drain end is not lower than the main pool drains but it's only about a foot higher than the shallow end, lower than the skimmer/vacuum line would have been where it was bobbing/resting in the shallow end. I'm wondering if, even though the pump was off, I had a siphon effect going and siphoned the water off through the vacuum hose, through the pump and out the waste line. It would have continued to siphon out until the water level dropped down far enough that the vacuum started bouncing out of the water, allowing air into the line and broke the siphon. Does this sound like something that could have happened? Could this be a reasonable explanation for where approximately 4,800 gallons went overnight? I should mention that water sat in the pool since last November with no apparent leaks and that I trust the pool installers implicitly. There are no apparent wet or swampy spots in the yard which I would expect to find if I had 4,800 gallons leak out somewhere.

Thanks for any information or assistance anyone may be able to provide.

- Byron


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