Help! Fiberglass pool leaking from main drain and skimmer after rains

Hey all. This is my first post on these forums. I am posting out of desperation and exasperation.

I have an 11 yr old in ground fiberglass pool (10k gallons) that has suddenly developed rapid leakage. I first noticed it after we received several days of rain. Prior to this everything was great. I went through every self test I could to help exclude all possibilities. I checked each opening with dye and found nothing. What I have noticed is that with all the return lines capped including the cleaner line and with ONLY the main drain open, my pool leaks 2 inches a day. I had a leak detection service out last week to pressure test lines. They apparently found a leak in the skimmer as he tested it at 30 psi and it quickly dropped pressure. Ok, so that means he has to come back and dig up the concrete and replace the skimmer to a tune of almost 1k bucks.

However, I mentioned my concerns for the main drain leaking. He tested the main drain and said it was holding pressure and that it was NOT leaking. At this point I kind of took his word for it. So presently, I have the main drain open and all else plugged again because I want to verify for myself. Again, pool is leaking 2 inches a day. There has got to be a leak in the main drain someplace I am thinking. The main drain is in the deepest part of the pool against the wall and does not lie flat on the bottom. I have been reading that hydrostatic valves often times become problems causing leaking over time.

One question I have is, does my pool even HAVE a hydrostatic valve? I live in north florida and would think so but apparently the original pool builder does crap building per the leak detecting service so who knows. How would I know or access it. I only have a 1 1/2 inch drain so I cannot access anything "within". Secondly, would my pool have a equalizer line in the skimmer? The skimmer has 2 drains built in but one of them is capped off so I am thinking it does not have an equalizer line. I am just trying to troubleshoot. I've scoured the internet for weeks trying to find some answers with no luck so this is a last ditch effort to see if someone else's experience/expertise can shed some light on this question. Before I shell out a $1000 to replace the skimmer I want to know that the main drain is not leaking. The pool guy says no, yet it STILL drains rapidly.

The only reason I am asking about hydrostatic valve is that it first started after several days of rain after a period of dryness. It rained for about 5 days off and on straight. When the pool was built, it was necessary to 'build up" where the pool was going to be placed as it was slightly sloped.Our home does settle as there are signs of cracking throughout the home and I am sure the pool is no exception. Are hydrostatic valves typically placed within the wall or underground someplace? One other thing I should mention is that my pool does have a spa that overflows into the pool. It gets it's water source from the main drain only. If the main drain is plugged I cannot run the spa.

Here's the bottom line- Would I have a hydrostatic relief valve? Is there a common connection between the bottom drain and the skimmer line? Would this line meet up jointly at some point then diverge again going back to the pump?

Any help and suggestions would be most helpful. I am totally over having a pool!! Thanks everyone.

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Originally Posted by mr2step

it [ the leaking ] first started after several days of rain after a period of dryness. It rained for about 5 days off and on straight. When the pool was built, it was necessary to 'build up" where the pool was going to be placed as it was slightly sloped.Our home does settle as there are signs of cracking throughout the home and I am sure the pool is no exception.

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Finding THE pool leak is hard, even when you are at the pool deck. Trying to do it via forum posts is nearly impossible. It's easy to find *a* leak; it's hard to know if *a* leak is *the* leak. It's quite common to fix several leaks and discover -- after fixing them -- that none of them are *the* leak! I'm in the middle of this right now, on a 200,000 commercial pool.

But, your paragraph I quoted above really, really concerns me.

Fiberglass pools are VERY light, relatively speaking. If the ground water level gets even a few inches above the level of the water in the pool, the pool can literally float out of the ground. Here's an extreme case, involving a concrete pool, posted on my Facebook page. In this case it's easy to see. But if your pool lifted 2 - 3", and then settled back, you might not see it. But you still might have a bunch of cracked pipes.

Putting lightweight pools (FG or liner) in wet sand is something of a risky business.

A hydrostatic valve is installed to prevent the sort of pool pop shown on the Facebook page. But it's function depends on being installed in a HEAVY pool, like a concrete pool. Because it takes so little hydrostatic pressure to lift an FG pool, a hydrostatic valve is unlikely to open and relieve pressure. Hydrostatic valves do sometimes open, and then 'stick'. To check someone has to SCUBA down, and remove the main drain cover, and check. But again I think this is unlikely on an FG pool.

Thanks for the input. Yeah I could understand why you would think about the pool "floating" however I don't think that is the issue, though not saying it isn't a possibility for this reason. We have amazing soil so drainage is outstanding. We rarely ever have standing water unless we get heavy rains of like 3-4 inches an hour but even within an hour of stopping the puddles absorb. I have also never had this problem before after rains so it probably would have happened by now in the 12 yrs since install I would have thought. The reason I ask about the hydrostatic valve is as you mentioned. I had read it can get stuck with possible debris or just get old and then let water out. The problem is which I mentioned in the OP is that I only have a main drain in the deep end but it is in the wall. There is no access to the piping other then the 1 1/2 pvc pipe opening. This is why I cannot tell if we even HAVE a hydro valve or not to access. My pool is leaking and it is sudden as I mentioned. It holds 30 lbs of pressure with the exception of the skimmer which does now. I know that leaks. But the drain is also leaking which DOES hold pressure per the pool guy as do the return jets. The funny thing is that it leaks 2 inches day via the drain when NOT running. I am noticing bubbles in the suction lines so am thinking maybe a suction leak somewhere? Would that be possible? Would a suction leak not be detected on pressure testing? I am just looking for some information. I am sure there may be more then one leak and am not using this forum to "diagnose" the leak but just for information on possibilities to look into. Thanks for the input!
Also, do you think it is possible for the main drain and skimmer to share a common line until they branch off again headed back to the pump?

Hydrostatic valves only open when the pressure OUTSIDE and UNDER the pool is considerably greater than the pressure INSIDE the pool. This can only happen when ground water levels are a foot or more higher than pool water levels. So . . . if your soil drains like you say, any hydrostatic valve could not have opened.

Put another way: conditions that would open the valve, would be even more likely to float the pool!

If it leaks MORE when the pump is OFF, than when it is on, it's even more likely you have a cracked underground suction line. In such a line, when the pump is ON, the pressure inside the pipe is reduced, thus reducing the leak.

. . . Still sounds like a popped (floated) pool to me.