Large volume water leak on our in-ground Fiberglass Pool

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Don in CA
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My Pool: In-ground 16.5’W x 36’ L with a 3’ shallow end and 9’ deep end San Juan Fiberglass pool that’s 30 years old. There is also a 7’ octagon in -ground Fiberglass jacuzzi upstream of the pool that gets a slipstream of water from the equipment and has a 1.5” overflow into the pool. The surface equipment was upgraded 7 years ago with a Pentair Intelliflo 3 HP Variable Speed Pump, Pentair 48 FNS Plus DE Filter and new 3-way valves & piping.

Large volume water leak on our in-ground Fiberglass Pool

Postby Don in CA » Thu 21 Jul, 2022 23:14

Hello, my name is Don Boydston I live in the Central Valley of CA. I am new to this site but I'm hopingthat this
forum will provide me with some informed advice on how I need to approach the upcoming repairs that are going to have to be done. We have a San Juan Fiberglass in-ground pool that is 16.5' W x 36.5' L and it's 3' in the shallow end and 9' in the deep end. I have what I believe is a critical issue with a substantial leak that I'm certain is in or around the main drain nozzle or line outlet from the pool. I noticed that this last week, the water make-up system was running continuously when the pool equipment was not. I shutoff the make-up water and had the pump running for the scheduled daily runtime.
Overnight the level dropped about 16" in little over 12 hours. I marked it and continued to monitor it's level and it continued to drop until it was pretty much empty at the Main Drain cover in the deep end within three days. The pool holds about 28 to 30k gallons of water so it is a substantial leak.
We had a leak about 10 years ago at the transition from the shallow to the deep end that we couldn't see (looking down from the deck) but the shell had a crack that was about 6" long but it was easy to see once the leaking water level got down to it and we could enter the pool. I believe that it was due to my wife and kids overfilling the water manually when I was working offshore and I was gone a week and home a week at a time. This was prior to me installing the water make-up system. It washed away some of the base (sand I believe) around the outside of the pool creating the stress crack on the shell. The technician made the repairs on the crack and there have been no other issues since then.
I have been using an electric Nautilus pool sweep and so the Main Drain 1 1/2" threaded port in the skimmer box from the drain at the bottom of the deep end has been plugged off for about the last 4 years with no issues. My understanding is that leaving the pool empty is one of the worst conditions that you can have as far as potentially creating more adverse issues with a fiberglass pool. I have scheduled a leak detection tech to come check the integrity of the Main Drain line but his soonest available appointment date is in about 1.5 weeks away and the fiberglass coating guy is telling me that it'll be 8 - 12 weeks until he can come do the coating and repairs. I don't think that I should go anywhere near that long with no water in the pool without potentially having more additional problems. So I have a couple of questions I'd like to get some responses to if possible:
1) I had no control over watching the level of water drain out of the pool but it allowed me to hopefully identify the location of the leak, but is there a maximum amount of time that I can have the pool empty before there may be more damage happening? I do NOT want any bulging on the side walls if I can prevent it.
2) Should I assume that it's the Main Drain nozzle/line in the bottom of the pool that is leaking based on where the water quit draining out and just plug the nozzle r opening off since it'll still be OOS after the repairs are made and I see no reason to put it back in service? I would be able to refill the water sooner and hopefully minimize the potential additional damage to the shell.
3) Are the timelines that my guys (they're both highly recommended for their quality of work) too far out that I should look for businesses that may be available to come do the work sooner?
4) We are considering doing some upgrades, especially if the pool is deemed "unrepairable", due to it's age. Is this the time to try to do them or should I get it all back in service ASAP so that I can price & schedule the modification work further down the road with a little more preparation time?

Thank you in advance for your advice I'd rather have professionals advise me on how to proceed.


Teapot1
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My Pool: 12000 gallons vinyl liner,

Re: Large volume water leak on our in-ground Fiberglass Pool

Postby Teapot1 » Fri 22 Jul, 2022 10:40

I would definitely plug the main drain to see the effect as its a cheap thing to try and would help the pool engineer to identify the problem and it saves valuable water.
I may not give you the answer you want to hear, but I will give an honest opinion of your situation as you decribe it.

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