Pool leak Main Drain? Next steps?

[EatsManyHotDogs]

Hi long time listener, first time caller here. I have a 10 year old, 20,000 gallon inground pool, vinyl liner. Winterized it myself last couple of years, with this year's winterization completed about Sept 1. Since then I've lost a steady amount of water, probably about 12,000 gallons. I look carefully for a hole in the liner but no dice. Decided about a week ago to pump out the rest of the water (too cold to dive in) and plug the two main drains with rubber expansion plugs. Yesterday I completed pumping about 8,000 gallons of water back into the courtesy of the local high water table and sump pit in my basement. My local pool store expert suggests that it could be a leak in the main drain piping, or the gaskets at the main drain. If the water level recedes, its a failed gasket. If the water level maintains, then its a leak in the main drain.

I plan on monitoring the water level closely over the next few days. Wife is urging me to call a pool leak repair professional but I'm too cheap. Is there anything else I should be doing in terms of troubleshooting?

 

[AftonJeeper]

Be very careful lowering the water in vinyl liner pools, it can cause the liner to shift. It is suggested to leave at least 1 foot of water in the shallow end to prevent this.

Many pools have a non working main drain, they are not necessary. So if it is not the gasket they just plug the drains and shut off the valve and you should be good next spring.

 

[EatsManyHotDogs]

thanks Afton, the liner may have indeed shifted. it was hard to tell since the water was murky. I am hoping it won't be too out of shape once I get the water level up to where it should be.

 

[Swampwoman]

I've been told recently that most liner pools don't actually have a hydrostatic valve in the main drain, but mine, which was built in a high water table area with sump, does.

Just so you know, IF your MD actually has one, these can get stuck a bit open by debris, etc. and cause the kind of leak you're describing. Its about a $20-30 part.

If you can access the original builder to find out, or if its specified in your docs, or if it leaks and you can dive down in spring to check it out, there are some good YouTube videos showing underwater change out of valve and how to dye test, so you may wish to google same.

 

[PoolguyinCT]

You can also order a waterproof inspection camera for 100 bucks off Amazon & get a good look into the sump from the deck... that's how I do it.. leaves over a MD can pop open the hydro..

 

[Swampwoman]

^Excellent suggestion

 

[PoolguyinCT]

At 10yrs old - draining major risk, i will be quite surprised if liner can handle the refill..

 

[EatsManyHotDogs]

Thanks for your comments. I'll check out the camera option for sure. If I had known about hydrostatic valves when I had the pool built 10 years ago, then I would have opted for it, but my builder was just looking to get in and out quickly and never mentioned it. So the issue will definitely not be a failed hydrostatic valve though I appreciate the idea. I'll cross my fingers on the liner handling the refill. I figured there was a good chance I would have to replace the liner anyway, and since I had already lost most of the water, pumping out almost the rest of the water to try and solve the issue was worth the risk. Maybe that was not the right move.

I'm not 100% sure of the accuracy of the measurement on the water level I took yesterday, but it appears the water level is down an inch today. I'll take another measurement tomorrow and report back.

 

[EatsManyHotDogs]

water level down 2 inches in 2 days. maybe it is the gasket after all. puzzling.

 

[Swampwoman]

Maybe you do have one after all? Here's a video of a diver changing it out. replacing hydrostatic valve - YouTube

Maybe if you use the camera idea you could determine if there's a valve in your md...or just a plug where the valve would be.

 

[EatsManyHotDogs]

drained the pool again today. no sign of holes in the liner. replaced the main drain gaskets. Also replaced the plastic seal rings (two of them, one on each main drain). I noticed the rings were a little wavy from the bolts being torqued down too tight. Not sure if that was the problem, but wavy is not as good as flat when it comes to seal rings and gaskets. I definitely do not have a hydrostatic valve, just a plug where that would go. Filling up the pool now. will measure any water loss and report back. Fingers crossed that the gaskets are the source of leakage, but honestly I didn't see any sign of failure.