In ground pool leak

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C

coilerman

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Bronze Supporter
Sep 29, 2008
169
Toronto, Ontario, Canada
I have a gunnite inground pool. It's been running fine for 7 years then about 2 weeks ago, I noticed that there was about an unusual water loss overnight.

I re-filled the pool and tried it with the filtration off and on and the same. About 2 to 2.5 inches gone in a 24 hour period. I tested the evaporation effect by leaving the spa filled and it only looses about 1/2" in the same period.

There are no leaks in any of the pipes above ground.

I suspected the underground plumbing so I let the water go down to below the level of all the outlets thinking the water loss would stop. But it keeps dropping.

So I figure it's the main drain. My first question is - what does the main drain actually do? I don't know that it's actually connected to anything. One explanation I got was that it's just there to equalize pressure. I don't really undersand this.

Secondly, I'm thinking I'll have to go for a swim and cover the drain with some plastic and see if it stops the leak. Thoughts?
 
If you find that it is the main drain, it can be plugged and abandoned. There is either a separate suction line from the drain to the pump (with its own valve) or it is plumbed through the skimmer. In the bottom of the skimmer there are two openings, one is the line returning water to the pump, and the other is connected to the main drain. To abandon the main drain that line is plugged at each end.

Having a main drain improves circulation and provides for draining without the need for a separate submersible pump.
 
I went for a rather unpleasant swim (water is green now from lack of circulation) and tried the dye test with some food colouring around the main drain. There doesn't appear to be any water loss around the drain.

Also, I had no water loss yesterday. This means the only possible culprit is the pool light. Right now, the water level covers about 1/3 of the light so I'm going to refill so the entire light is covered and see if I get the water loss tomorrow.

I'm really hoping the light is it. If not, it has to be the actual pool vessel itself. What is the likelihood of that in a concrete/gunnite pool?
 
A leak in the main drain is very rare. I do leak detection on about 10-15 pools a week and I hear customers tell me that they suspect leaks in certain places but they hardly ever are where they suspect. First off get your dye syringe out and check your skimmer, and when I say skimmer we are talking about the throat. The flow of water erodes the grout lines and causes many leaks. The 2nd most likely spot is in the light housing. Since 1998 they have been putting plastic light housings in pools and they crack all the time. There is one screw at the top and a hinge in the bottom. Look around the conduit for a crack. A good way to check your plumbing lines fast without pressure testing is close the valve at the pump, cover all but one opening in the pool with duct seal (1.99 at Home Depot), and spray your dye but the one opening that isn't covered. If the dye moves back and forth, that's normal, if it sucks it in you have a leak. If you have any other questions go to my website and look at the info I have on it.
 
How strange -- after posting the video link above yesterday, I felt the urge to don the mask and snorkel and go around my pool with dye testing things. Wouldn't you know it, I found a small leak around one of the return outlets. I had a suspicion that the water loss rate had changed recently, and now I know why. I'm losing about 1.5-2" in a week's time -- a bit faster than normal evaporation rate.

Off to the pool store for some a+b epoxy putty.
 
If the leak is in the skimmer throat and its a grout line we use 2 part pool putty. If its in a plastic skimmer throat we use marine 5200 caulking (available at any hardware store). No matter what the repair or what you are using to repair the leak, the key is prepping the leak. If its a plastic crack use a wire brush first to get the grime off, then hit the plastic with wet/ dry sandpaper. If you are repairing a grout line and using 2 part pool putty, chip out any lose grout, then hit it good with a wire brush. It is very important that the 2 part putty is mixed very good and evenly. Get the putty wet a couple times when you are mixing it to loosen it up a tad and get it mixed well. Do not run the pump for 24 hours after repairs. If your repair is messy when it dries hit it with sand paper or a wire brush to clean it up and make it even.http://www.youtube.com/watch?v=BRsHpaSiKcI This is a good video of where to look in your skimmer.
 

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Patching around the return pipe was remarkably easy to do with the a+b epoxy putty. I scraped the plaster around the pipe and it crumbled into a void hiding behind the skim coat of plaster. Worked the epoxy into the larger void and that sealed it right up.

Does anyone have any expectation on how long this type of underwater patch job is going to hold up?
 
The time that the patch holds is relevant to how good you prepped the leak and how good the putty was mixed. Let a few days go by and try to dig your fingernail into the putty, if your nail goes in and it crumbles then the putty wasn't mixed properly. In my experience (I do leak detection on around 15 pools a week), patches hold for around 2-5 years. A patch like you are talking about will hold for a long time because it has no direct water flow on it.
 
Update: I was wrong in my previous post. I let the pool sit for a few days and either the leak returned or I didn't measure properly the first time.

I kept letting the water go down below each shell intrusion and each time, the leak continued.

1) below the skimmer
2) below the return lines and vacuum port
3) below the pool light

Each time, the leak continued. So it has to be the main drain. I dove down and threaded a teflon coated plug into the pipe that goes from my main drain to the skimmer. It still leaked. Visual inspection of the plug at the bottom of the drain shows no cracking or decay of the expansion plug.

I now have the pool completely drained. I filled the bowl of the main drain with clean water and I'm watching what happens.

This thing has me totally stumped.

On a side note, with the water out of the pool are there any maintenance tasks i should perform? What do I use to clean the gunnite other than water and a scrub brush?
 
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