How much water loss is normal?

dancingsamsApril 29, 2010


We have a 25 x 50 foot pool, plus splash area, with a negative edge. We measured and marked the level in the pool and trough at 6:15pm, and turned everything off. The next morning we recirculated the water (water had leaked from the pool into the trough), turned everything off again and remeasured. Since it is a negative edge, the loss showed up in the trough. It was down 4", or 374 gallons in just 16 hours.

Our PB says this is "normal". We think it is ridiculous.

Please - any thoughts?

Thank you!

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4" seems like a lot, but the test is: Use the bucket test.

Fill a bucket to the same level as the pool water and let it sit in the pool - say on a step. If it's evaporation, both will drop about the same. If the pool varies noticeably from the bucket, then the pool is leaking.

    Bookmark   April 29, 2010 at 2:42PM
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The bucket test won't work for a negative edge pool. You can end up losing quite a bit of water to evaporation over the weir. I'd keep the pool off for 24 hours and see how much change their is with no water movement. Still 11000 gallons a month does seem pretty out there.

    Bookmark   April 29, 2010 at 3:03PM
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Thank you,

dkv-texas - our test was with the pool, filter, etc all off. We lost 4 inches in the trough in 16 hours. The trough is 3 feet wide by 50 feet long. Using math, we calculated the loss to be a total of 374 gallons in those 16 hours. Also, the pool cover was on (so evaporation was reduced somewhat - the cover only goes over the rectangular 25 foot by 50 foot section). Does this make sense?

    Bookmark   April 29, 2010 at 3:34PM
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All systems off and a 4" drop? That's about a quart and a half per minute. Are there any visible signs in front of the trough?

How deep is the trough?

Is there an overflow outlet in the trough?

Is there a surge tank?

Is the trough finished with plaster or just raw concrete?

Dye test the drain edges and inside the pots and any other openings in the trough.


    Bookmark   April 29, 2010 at 4:08PM
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Hi Scott,

The trough is about 4 feet deep. It has an overflow, but the level is, and was before our test, below the overflow by more than an inch. It is finished with pebbletec. We do not have a surge tank.

How do I do a dye test, what kind of dye, and what are pots? Can you tell I'm a novice?

The openings in the trough consist of the overflow (not in question, since we are below that level), the drains for the cleaning system, and a water leveler that moves water between the pool and the trough. Also, the spa overflow empties into the trough. We have a Caretaker built in pool cleaning system (that we believe is not functioning properly). There are 5 drains in the trough for the cleaner, but only 2 have suction when the system is turned on.

This is a complex pool, with a pb that keeps making silly statements, such as "that much loss in normal", and that we didn't need the caretaker system to work since he gave us a polaris 280.

    Bookmark   April 29, 2010 at 4:27PM
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Within a couple of minutes of turning off the system, the trough's water level should be stable, assuming no air leaks to drain the plumbing.

Is the equipment pad at pool height of trough height?

How many pumps is your system comprised of? Do you know what each does?

The statement in the original post, "water had leaked from the pool into the trough" is confusing. How did this happen? Had you marked the pool level too?

Is there an auto fill? If so, is it electronic or float operated?

Where does the water go when it reaches the overflow in the trough?


    Bookmark   April 29, 2010 at 5:42PM
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Hi again,
The equipment pad is at pool height.
The system has 3 pumps. One is for the spa, the other two operate the pool. We have asked many times and have yet to get a clear answer as to how they work. My husband is an electronic engineer - highly respected in our industry, which is NOT pools. He is quite frustrated!

We did mark the pool level, as well as the trough level. We measured with a measuring tape, and also put masking tape on both the pool and trough to mark the starting point.

There is an auto fill. It is electronic. We turned that off prior to marking the levels, and left it off during our test.

If the trough gets too full, the overflow drains onto the ground away from the pool.

By "water had leaked from the pool into the trough", I am trying to say that initially the pool was level with the negative edge. The next morning, in order to get an accurate reading, we ran the edge pump enough to get the pool level with the edge once again, then measured the difference in the trough.

I am trying to post pictures, to see if that might help.

    Bookmark   April 29, 2010 at 6:21PM
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Night 1) System shut down, auto fill included. Water level at the weir.

Next Morning: Water below the weir in the pool. How much?

Water level in trough is elevated. How much was it elevated? Was it still below the overflow?

Do the pool and spa have separate filters?

Does the weir only function when the floor system is on?

Do the lamiter jets function off the floor system pump?


    Bookmark   April 29, 2010 at 6:39PM
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Hi Scott,
Please - what is a weir? If it is the negative edge, then yes, the water was below the weir in the morning. The pool was down 1/4 inch, and the trough was up over an inch (but still below the overflow).

The pool and spa have separate filters, as do the water features. The laminar jets have a separate pump system.

The edge pumps can run without the floor system being on.

Did I miss anything? :)

    Bookmark   April 29, 2010 at 7:00PM
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You need to compare the square footage of the entire structure (pool, spa and trough) with the square footage of the trough alone. The depth or volume of the pool, spa and trough have nothing to do with this calculation. If for example, the total surface area was 1500 square feet, and the trough was 250 of that, normal evaporation of .25" would translate to a loss of 1.5" in the trough, and also remember that negative edge pools typically evaporate more than conventional pools.

    Bookmark   April 29, 2010 at 7:14PM
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Do your testing with the autofill off, first with the pump running for 24 hours, marking and measuring the level in the trough, then with the pump off, every valve on your equipment pad closed, marking and measuring the level in all the bodies of water. The results of these tests will help determine if you have a leak and also where to start looking.

    Bookmark   April 29, 2010 at 7:28PM
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I have a neg edge a little larger then yours and I do lose more water then a conventional pool.
You are losing less then a 1/2" of water a day. That does seem a little high but there are many factors. You said you have a cover, with that your evap rate should be much less.

You should do a bucket test. Turn everything off. Splash down enough water into the trough so wind will not splash any more over. Then start your bucket test.
Put a bucket on the top step and add pool water so it is the same level inside as well as out, flashlight works well for this. (you may need to add a rock to help with ballast.) They should evaporate at the same rate. If the pool goes down more then you have some sort of small leak.
Check the trough as well, you can have a leak there as well.
The most common non piping leaks occur around a skimmer, and any penetrations, every infloor head, maindrains, returns ect.

    Bookmark   April 29, 2010 at 9:20PM
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So far, it sounds like a wind blown difference and a possible leaky check valve. A stiff breeze can blow some water from the pool into the trough. A check valve that doesn't seat as positively as it could may leak a small amount too.

Since the pool is higher than the trough and water seeks it's own level, a trace reverse flow may account for the pool lowering the 1/4 inch but I would think that that would raise the trough level more than the single inch.

Could the trough have been more than an inch higher?


    Bookmark   April 29, 2010 at 9:27PM
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My wife and are having this are actually having a conversation right now re; one of her client's negative edge pools. Most of the HOA'S here require that pools built on a lake (man-made or not) must have a infinity/negative edge. Poolguynj is correct. The most likely problem is the check-valve(s). We see this a LOT! What happens is that the trough tends to be a catch-all. Debris on top of the pool that doesn't make it into the skimmer ends up in the trough. Wind blows debris up hill from the lake and into the trough too. As most negative edge features run on a separate pump, they usually have no filter. Also, most N.E.'s drain covers don't prevent smaller debris from making it to the pump. That leaves only the pump basket to catch any thing that gets sucked into the suction lines in the trough. Anything too small for the pump basket to catch goes back into the pool and often gets hung up in the check-valve on the way. If debris is caught in a check-valve (before or after the pump) or if the diaphragm of said check-valve is damaged, this WILL allow water to flow in reverse (from the pool into the trough) once the pump shuts off. If the pool is 10,000 gallons and the trough has 200-300 gallons, the pool can drop 1/2-1 inch and over flow the trough. Water does indeed seek it's own level. I say, "Check those check-valves". :D

    Bookmark   February 4, 2011 at 11:35AM
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