Pool Leak Mystery - Help!

[Nanos203]

Hi Everyone, This is a bit of a long story but hopefully the information will be helpful in troubleshooting my problem.

I inherited a 22,000 gallon Hallmark Hybrid pool when I purchased my home two years ago. It is kidney shaped, the walls are fiberglass, and the bottom is concrete with plaster. Apparently it was sold to builders as a pool kit to home builders used back in the 70's. I believe the pool is about 40 years old based on city records.

Anyway, I had never owned a pool before and this pool hadn't been opened in about 10 years. I had it cleaned out, patched up, and lines pressure tested; main drain was fine and skimmer lines had slow leaks. I replaced the skimmer and return lines. I opened the pool last summer and have had a "slow" leak ever since. I've had to top off the pool every two to three days (about 700-1000 gallons a pop). I have tried to find the leak on my own using dye but without success. So I decided since the season was over to let the pool drain. I closed off the skimmers when the water had dropped below them. One morning, I came out to find that the pool had drained about 18-24" over night as opposed to the "normal" inch or two. I observed that the main drain was covered with leaves so I turned off the pump and removed the leaves. After that, the pool resumed it's "normal" water loss rate (pump off at this point because I couldn't regain prime). I'm baffled by this situation and at this point I'm continuing to let the pool drain; the shallow end is completely empty and the deep end about half way. I'm guessing the leak is from either the main drain or the drain plug (the plug that releases hydrostatic pressure when removed). Thoughts on what what's going on and what I should do? I am also a bit worried about the implications of 22,000 gallons draining beneath my pool as my pool becomes emptier and hence lighter. Thanks in advance for your help!

 

[prs]

Was the pump running overnight when you lost the 24", and pumping just from the main drain to the returns? Does the main drain go directly to the pump or is connected to a skimmer?

24" is a lot of water, it must have gone somewhere and left a trail, is there a washout area or very muddy ground that will give you a clue as to the location of the leak? If that major loss of water left no signs is it possible the water was pumped to a drain by mistake? What kind of filter do you have?

Is the water level in the pool still going down faster than just evaporation with the pump off? If so the water must be going somewhere and finding where it is going might give us a clue.

I'm not sure what you mean by the hydrostatic drain plug, is this a hydrostatic valve that allows ground water to enter the pool from the outside whenever the level in the pool falls below the ground water level? If so it is quite likely the valve is not seating properly and needs to be flushed out or replaced. Does it look like this?

http://www.aquapure-il.com/Hayward-hydrostatic-relief-valve-plastic-1-1-2.html

Let's hope it's the hydrostatic valve, that's an easy fix!

 

[Nanos203]

I am continuing to lose water; at this rate, the pool should be empty in 3-4 days.

When the large water loss occurred, I believe the pump had been running for about 12 hours pumping from the main drain to the returns. I was able to regain prime with difficulty for about a day after I cleared the leaves from the main drain and the pool lost it's "normal" amount of water. After that, I turned off the pump altogether. It appears that outside of the huge one-time drop, the pool loses water at the same rate regardless of pump on or off. I do not believe that the main drain is connects to the skimmers.

24" is a ton of water and I did not see any obvious trail of it. It definitely didn't get accidentally pumped to waste as a) the waste line has a separate valve that remains closed, and b) if that valve somehow had failed, my dry-well would have overflowed and I would have noticed the flood.

I don't recall seeing a hydrostatic drain plug when I took a look at the main drain when they had repainted the pool. I recall seeing two holes-- one with piping that goes back to the pump and the other with sand (presumably the sand beneath the pool?).

Thanks for helping me troubleshoot this mystery!

 

[prs]

If the leak empties your pool completely it must be below the level of the pool floor, either at the connection of the main drain to the floor, or in the main drain pipe as it runs under the floor. However you said that the main drain line pressure tested OK two years ago, so let's lrule out any other possible causes before we say for sure it's the main drain.

I'm a bit confused about your hydrostatic drain plug as described in your first post

I'm guessing the leak is from either the main drain or the drain plug (the plug that releases hydrostatic pressure when removed).

In your second post you say

I don't recall seeing a hydrostatic drain plug when I took a look at the main drain when they had repainted the pool. I recall seeing two holes-- one with piping that goes back to the pump and the other with sand (presumably the sand beneath the pool?).

Could you be more clear about the location of the drain plug, and where exactly is the hole with sand.

It looks like your ground water table is below the level of the pool, orherwise the pool wouldn't drain, so no danger currently of your pool being floated out of the ground, but I'd be concerned if you were suddenly to get heavy rains. Another reason why we need to know more about this hydrostatic drain plug.

Also was the pool filled after you had the lines pressure tested or did it stay empty during a winter freeze?

 

[CUTiger78]

... I recall seeing two holes-- one with piping that goes back to the pump and the other with sand (presumably the sand beneath the pool?)....

I hope the sand you saw was some sandy debris that accumulated over time on top of the plug in that hole. If the sand you saw was the sand beneath your pool, then you've found one leak.

Good luck!

 

[Nanos203]

So I pumped out about ~3.5ft of water and removed the main drain cover. There is about 8" of water left. There is a main drain pipe and a hydrostatic valve with a big H on it (I guess they installed that after I had last looked at it). I put some dye into and around the main drain cavity and the dye seemed to stay put! At this point I'm baffled. Any ideas other than calling a pool professional?!

 

[Nanos203]

The water is still draining. I'm going to cap the main and see if the water still drains. If it does then it's the valve; otherwise it's the main.

 

[prs]

I'm assuming you have carefully checked the floor and sides of the pool that were below the water line before you pumped and haven't found any cracks? Also I'm assuming the water level was still falling when you decided to pump? If the level had stopped falling it might have given you a good idea where the leak might be.

At this point I think you can tackle two possible causes of the leak.

1)Let's start with the hydrostatic valve, it's possible this valve is not seated properly. If you google "pool hydrostatic valve" you'll find lots of info on these valves, including a video of how one was replaced. You may choose just to flush out the valve and make sure any seating surfaces or gaskets are in good shape and free of debris, or you could replace it with a new one, or you could just replace the valve with a plug to make certain it never leaks again. Of course if you decide to plug you'll have to be extra careful whenever you drain the pool.

2)Second to check out the main drain piping first determine the size of the pipe at the main drain and then go to Home Depot and get one of these

http://www.homedepot.com/p/Oatey-2-in-Gripper-Mechanical-Plastic-Test-Plug-33401/100346775

Insert it into the main drain and tighten the screw to plug the line, then you will be able to fill the pool to maybe two or three feet at the deep end and check if the leak is fixed.

If the water level still goes down then most likely you have a crack in the floor or wall somewhere.

If the water level doesn't go down, remove the drain plug from the main drain, and again check to see if the level goes down. If the level doesn't go down your leak was likely the hydrostatic valve and the problem is fixed.

If the leak comes back when you remove the plug then the leak must be in the main drain piping.

Edit: I see you posted the solution while I was putting my post together.

 

[Nanos203]

So it was the hydrostatic valve after all-- it was stuck open! I cleared it of debris and now it smoothly opens and closes. I marked the waterline and will check it in a few hours. Then I am going to do the same with the main drain line-- do you think it's worth having that line pressure tested again now that the pool is empty?

 

[prs]

Glad you found it!

The fact you could get prime on the pump even after the 24" drop in pool depth is a pretty good indicator the main drain piping is fine. I guess uou could check it by plugging the line at the bottom of the pool and then filling it with water at the pump. If the water level at the top of the pipe doesn't drop, you should be golden.

I bet the leaks in the return and skimmer lines you found when you bought the house were caused by the pool not being properly winterized.

 

[Nanos203]

Turns out that in addition to the valve being faulty it the area around the fitting was cracked which I fixed with an epoxy. I was also having trouble getting a good seal on the new hydrostat using thread tape so I used this product which formed a good seal. No more leaking down there.

 

[Nanos203]

all good!