Pool Leaking - A Good Mystery So Far

[guitarzombie]

I have a leak in my 4 yr old vinyl pool liner. The pool is over 20 yrs old. (see pool data below). I have been taking "pool water level" data for the last 4 days. The pool, with about 3 feet in the shallow end, was leaking 0.1" per hour when I started measuring it. After 4 days the leak rate is down to 0.075 " per hour and has lost an additional 7 1/2" (about 3100 gallons). The bucket test shows almost no evaporation (high humidity here in Atlanta - although charting my data shows a spike during mid to late afternoon - see graph link below). I have ruled out the plumbing (the water is now well below the pipes and skimmer). I have ruled out the light and fiberglass steps using dye (checked several times - ughh). When I started measuring 4 days ago, I was losing about 1000 gallons per day and now I am losing about 750 gallons per day. There is now, perhaps about two feet in the shallow end and six in the deep end. I have inspected the walls and floor using a mask/snorkel and dye and can not find a leak in the vinyl liner. (FYI - At about 6 feet of water in the deep end, a hole will see about 2.6 psi). I am not sure how large of a hole I am looking for (and may run a test today with a 6 foot pipe and some vinyl at the bottom of the pipe and try to see what size hole could cause this - assuming it is one hole). The leak translates to, somewhere in the neighbor hood of, 1/4 cup per second. You would think that a leak this large would be easy to find. It has been around 90 degrees and fairly humid here everyday, and will not account for the water loss due to evaporation. A graph of my data for the last 4 days can be found at the following link: http://guitarzombie.com/pool/graph.jpg and I have added it as an attachment (but don't know how that works). So..... I will try to find the solution to this problem and will post my results, hoping it may help someone else someday, however any input will be appreciated. In the mean time, I think I am going to build my own electronic leak detector today (too cheap to hire someone). Oh..., if anyone is wondering where all that water is going - underneath my deep end is a plenum where I can pump ground water from under the pool. Thanks for reading.

Pool Data: 18' x 36', vinyl liner 4 yrs old, 4 foot shallow, fiberglass steps, skimmer, two outlets and a light, 8 foot deep, leak below plumbing and still losing water.

[guitarzombie]

Additional about my above stated problem leak: The problem may be that, either, I don't know how to leak test with dye, or dye testing doesn't always work, because the water stopped at the top of the light facing. I discounted a leak here because I tried at least 5 times to dye leak test it. prior to leak testing, I pulled the light out, that sits inside of a metal shell that is supposed to be sealed. The lamp wire goes through the back of the conduit - which emerges above my cement deck (under the diving board). I am thinking that the conduit may be leaking somehow between the shell and the emergence of the conduit above the cement, as the shell is one piece and I can not see up the conduit. I am going to drain the pool below the light and reseal the light and conduit (which was never sealed). I suspect that the conduit may have rusted over time. The following link is a sketch of my latest theory.

http://www.guitarzombie.com/pool/crosssection.jpg

I can not just seal it, I have to know what the problem is, so after I seal the conduit from inside, I will try some sort of leak test from the surface.

[ChuckGeo]

Sounds like you're on the right track suspecting the light conduit, it is a common leaker. The best way to seal it is with a product called Anderson's Butyl Tape. It is a sticky caulking compound that comes in a roll. You unroll the 1/4"X1/4" caulking strip and pack it in the conduit hole in the niche and around the light cord, real tight. It will seal the conduit, stop the leak and be easily removable if you ever have to replace the light. It's a better solution than sealing the conduit with epoxy or silicone, both of which can be difficult to remove down the road. You might also have a leak around the outside edge of the conduit fitting in the light niche. It's always best to confirm the exact location of the leak prior to repairing anything, then confirming that the leak is repaired, with a dye test, after you make the repair.
I'm in the Atlanta area if you need help.