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Thread: sink hole under liner, should i be concerned?

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    sink hole under liner, should i be concerned?

    I just put up an oval above ground pool a few weeks ago, and i did all the work myself. Everything is going really well so far. But there is one place under the liner at the bottom of the pool where a sink-hole developed after the pool was filled for a couple of days. Its been there for a couple weeks now and so far hasnt gotten bigger. The hole (dip) is circular, about 4 inches wide, and I'd say about 3 inches deep. At the top edges of the hole, it just kinda drops almost straight down, so the shape of the hole is almost a mix between a soup can and a bowl. If i push around in the hole, at the bottom i can tell that its not solid, the liner gives some, so the sand underneath has apparently sank even lower but the liner is stretched as far as it will go (for now). Should i be concerned about this? The liner is brand new, so i obviously want it to last for years. Its an oval pool which has the metal supports that go under the pool which get covered in sand. The hole looks to be near the end of one of the supports. So i'm thinking I didnt shove enough sand at the end of that metal support where the band attaches to the support on the opposite side. Either that or some of the sand around that end of the support somehow got pushed into the support itself when the pool was being filled (metal support is long and rectangular, with a hollow middle thats opened at the end). Either way, I'm not sure what I should do about it. Should i be concerned? I can deal with it looks-wise. I just dont want to have to replace the liner after 1-2 yrs because I decided not to do anything about it.
    15x33 AGP (somewhere around 11-12k gallons)
    1.5 HP Hayward PowerFlo Matrix Pump
    150 pound hayward sand filter

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    Mod Squad Bama Rambler's Avatar
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    Re: sink hole under liner, should i be concerned?

    At 4" wide and 3" deep I'd recommend you fix it. Especially since the edges are kinda sharp. Not that they will cut the liner but they will stress the liner and it may fail in that area. If it was a slight dish an inch deep I wouldn't worry about it.
    Dave J. TFP Moderator
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    Re: sink hole under liner, should i be concerned?

    I guess the only way to fix it would be to drain it, pull the liner up in that section, crawl in and repack? So trying to think what would be best...do it at the end of the season (maybe a month from now), and refill the pool 3/4 way after that...and then put a cover on top. Or drain it after the season, fix the hole, and leave the pool empty till start of next season....or something else?
    15x33 AGP (somewhere around 11-12k gallons)
    1.5 HP Hayward PowerFlo Matrix Pump
    150 pound hayward sand filter

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    Re: sink hole under liner, should i be concerned?

    Are u losing any water it sounds like a leak either you need to fix it I have seen aboveground liners with pin size holes that I personally took out of a box the problem was the home owner bought it over the internet you need to fill it to keep it from collapsing

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    Re: sink hole under liner, should i be concerned?

    not sure i understand you. Are you saying that you think the dip in the liner is indicating a pin-hole leak? can you explain more?
    15x33 AGP (somewhere around 11-12k gallons)
    1.5 HP Hayward PowerFlo Matrix Pump
    150 pound hayward sand filter

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    Re: sink hole under liner, should i be concerned?

    On aboveground pools most times when u find a intention like that it points to a hole go swimming with goggles on use your hand to swish away any dirt from the hole if there remains a speck then look closer at it chances are its a hole but it also could be the sand settling did u pack the sand when u were installing the pool

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    Re: sink hole under liner, should i be concerned?

    yeah i packed the sand. But the dip is near the end of one of the metal supports, so it could be possible that i thought it was packed good around the support when maybe it really wasnt.
    15x33 AGP (somewhere around 11-12k gallons)
    1.5 HP Hayward PowerFlo Matrix Pump
    150 pound hayward sand filter

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    Re: sink hole under liner, should i be concerned?

    Did u wash the sand under the plates if not that could be where the sand is going but check for a leak

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    Re: sink hole under liner, should i be concerned?

    i tried to, but again, i might not have done it perfect. But that is a good thought, there are metal plates that connect all of the metal supports on one side together. If lots of pressure is put on the sand next to the plate, I could see how it might push the sand under the plate, creating the dip.
    15x33 AGP (somewhere around 11-12k gallons)
    1.5 HP Hayward PowerFlo Matrix Pump
    150 pound hayward sand filter

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    Re: sink hole under liner, should i be concerned?

    So either way, it sounds like I'm gonna need to drain the pool and fix the problem, whatever the problem it is. Now, what is the best way to do that? Is it a good idea to leave an above ground pool empty over the winter? Seems to me it might be better to have water in it, but if i drain at end of season, i'll need to fill it back up to 6" under the lowest return (got that from pool school). But pool school also says to shock it for 24 hrs before you cover it. So I' either have to fill it all the way, shock it, and drain back down to 6" below lowest return, or fix the problem, fill to 6" below lowest return, and figure out a way to shock it with the water level that low (and not being able to use the pump)....
    15x33 AGP (somewhere around 11-12k gallons)
    1.5 HP Hayward PowerFlo Matrix Pump
    150 pound hayward sand filter

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    Mod Squad Bama Rambler's Avatar
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    Re: sink hole under liner, should i be concerned?

    I use the vacuum hose to siphon water out. You'd be surprised how fast that big ole 1" hose will move water.

    You can empty it and then refill it to the winterizing level (6" below the return) and hook the vacuum to the skimmer and use the pump to circulate the water so you can chlorinate it properly. It doesn't have to be full to do that.
    Dave J. TFP Moderator
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    Re: sink hole under liner, should i be concerned?

    good idea. I was thinking it'd be hard to keep it primed doing that. But if you say it'll work, I'll say i'll try it!
    15x33 AGP (somewhere around 11-12k gallons)
    1.5 HP Hayward PowerFlo Matrix Pump
    150 pound hayward sand filter

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    Mod Squad Bama Rambler's Avatar
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    Re: sink hole under liner, should i be concerned?

    Unless your equipment is above the pool a good bit it shouldn't be an issue getting or keeping it primed.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: sink hole under liner, should i be concerned?

    its sitting on the ground thats about level with the bottom of the pool, so it should work then.
    15x33 AGP (somewhere around 11-12k gallons)
    1.5 HP Hayward PowerFlo Matrix Pump
    150 pound hayward sand filter

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    Re: sink hole under liner, should i be concerned?

    Any pictures of where the sink hole is? Is it near the edge of the pool or in the middle?
    DIY 28x38x18 Full L, 26,000 gallons, Pentair VS Pump, SWG, CCP 420 Filter, Sta-Rite Max-E-Therm SR400HD Heater, EasyTouch Controller

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    Re: sink hole under liner, should i be concerned?

    I managed to get a picture of it, here you go. Its not on the edge, its kinda out in the middle. So i did some better estimating. I'd say its maybe just 2 inches deep. Also, (in response to ENCSOLAR's posts) there is a tiny spec in the middle of the dip. Although it doesnt really seem like the spec is a pin-hole, but I'm no pin-hole expert, so maybe it is. The spec is kinda grayish/shinyish, almost like a very very tiny spec of metal. But the feel of it is smooth, i can't feel any difference when touching it.
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    15x33 AGP (somewhere around 11-12k gallons)
    1.5 HP Hayward PowerFlo Matrix Pump
    150 pound hayward sand filter

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    Re: sink hole under liner, should i be concerned?

    That looks like a sink hole causes by a leak

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    Re: sink hole under liner, should i be concerned?

    take a little bottle of food coloring into the pool underwater with you...and do a few little "puffs" of the bottle right near that little spot you see..if you see some dye suck into that little hole..it's a leak..if it just floats past, then you have no leak. This method works very well.
    33' x 52" Swim and Play Inc. PARAGON AGP. Hayward H200 Heater. Hayward Power-Flo LX 1.5hp pump. Sta-Rite Cristal Flo T-210WF Sand Filter. Stenner 45M5 chlorine pump

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    Re: sink hole under liner, should i be concerned?

    Interesting idea, thanks! I'll give it a shot in the next day or two and report back.
    15x33 AGP (somewhere around 11-12k gallons)
    1.5 HP Hayward PowerFlo Matrix Pump
    150 pound hayward sand filter

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    Re: sink hole under liner, should i be concerned?

    Check this new post out:

    what-a-dye-test-looks-like-t69782.html
    15'x48" 4500 gallon Intex pool, buried 1.5 ft. Pac-Fab Dynamo 3/4 hp pump. Hayward S180T sand filter, bought used. Taylor K-2006 test kit. Rocket mass heater based wood fired pool heater.

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