My experience of time it takes to dissolve salt

[mjmeans]

My pool has an in-ground pop-up head cleaning system. The pool is about 11K gallons. The filter is a StaRite System 3. The pump is single speed WhisperFlow and has enough pressure and rate of water flow to operate my OLD Caretaker in-floor cleaning system at 10-12 PSI in the 5-port valve (should optimally be 15-25 psi, but it works fine as it is). With the SWG turned off and the in-floor cleaner turned on I add a 40-lb bag of Arizona's Own pool salt. This salt has a fairly fine grain size. The granules are smaller than kosher salt, about the size regular table salt. Pool temp is about 88 F. After 4 hours I can see tiny sparkling reflections in the water under direct sunlight, possibly tiny salt crystals yet to dissolve. After 6 hours I no longer see any sparking, but there is the faintest 'haze'. I test the salt level using Aqua Chek strips. At the 8-hour mark the haze is gone. I test the salt level again. There is a small difference in reading between the two salt tests. I think this is pretty much consistent and expected. I'm assuming the next 2 tests at the 10 and 12-hour point will reveal the salt level has stabilized. So even though online guides suggest 24-48 hours for dissolution and mixing I'm assuming that the specifics in my case, being very warm water and the effect of the in-floor cleaning system continuously "brushing", that 10-12 hours hits the mark for stable test results.

Is this consistent with other's experiences when adding salt?

Is there any chemical reason to think the salt test results shouldn't be considered stable and accurate at the first point there no visible salt in the water and two consecutive tests 2-hours apart have the same reading?

FYI, the reason I'm doing this this way is that my pool is a strange shape and I want to accurately measure the volume of water in the pool by observing the change in salt ppm with a given quantity of salt. The salt bag was weighed with a precision shipping scale at 40.04 lb and is labeled as 99.8% pure. So in principle, since salt doesn't evaporate, if the water level is maintained I should be able to calculate the water volume from the change in salinity at a given addition of salt.

 

[Orion7319]

Not sure about the pool volume thing. I don’t wait for my salt to dissolve. I dump it in and then use my pool brush to stir it around until it’s completely dissolved. Usually only takes around 10 minutes or so. Then I turn on the pump to its two hour quick clean cycle to mix it and forget about it.

 

[duraleigh]

I am not sure any of the salt tests are accurate enough for measuring pool volume with any precision. It's possible but I think there are too many variables as well as the tests themselves usually having a wide resolution.

I would suggest dividing the pool into shapes that you can use mathematically.

 

[mjmeans]

I did consider the potential for other variables on the reading accuracy of the tests, such as water temperature, TDS, CC, FC, Ph, etc which is why I'm doing this salt addition and multiple measurements of salinity all while all other factors, including wind and weather, are stable.

The only "flat" areas of the pool surface are the tops of the steps and three portions of floor around the two drains and the shallow landing of the steps. The continuously changing Bezier-like curves, usually changing in two dimensions at the same time, don't lend themselves to any mathematical geometric shapes. If the pool were empty, I suppose laser scanning could work. But I don't have that kind of equipment. When I had the pool resurfaced many years ago the company that did it based it on, IIRC, a 15k gallon pool. Historically it's been responding to chemical adjustments at somewhere between 10-12k so the resurfacing company possibly overcharged me by 20-30% for materials simply because it was so difficult for them to even estimate the surface area.

 

[Orion7319]

Historically it's been responding to chemical adjustments at somewhere between 10-12k so the resurfacing company possibly overcharged me by 20-30% for materials simply because it was so difficult for them to even estimate the surface area.

If it’s responding to chemical adjustments at around 10-12k, then you are good from a chemical dosage point of view, you can dial it to a greater accuracy by trial and error from there. If you feel like you were overcharged, that’s another matter. If you ever have to drain and refill the pool, you could get a much better idea by paying attention to your water meter.

 

[markayash]

I drained mine and refilled it last year and remembered Someone here suggesting watching my water meter.
I was told it was 18000 when I bought the house but it held 22000 gallons.

 

[mjmeans]

My water bill is in Ccf (748 gallon) increments. Not sure what the accuracy is, and I would guess that it's rounded up. So that isn't likely to result in a much better measurement than 10-12k gallons as far as accuracy is concerned. The previous and current reading value is in Ccf. It possibly does count individual gallons, but that isn't revealed. It is a good idea though. Just wouldn't work in my case.

 

[mgtfp]

My water bill is in Ccf (748 gallon) increments. Not sure what the accuracy is, and I would guess that it's rounded up.

You'd need to check your water meter on site before and after refilling, while minimising all other water uses during the refill. Going by the water bill wouldn't be enough, not just because of the 748 gallon increments, but also because you needed to estimate all the other water uses during the whole billing period.

 

[Turbo1Ton]

Personally, I would use liquid chlorine, or muriatic acid additions to try to dial in pool size. Those are both additions that get used up and are easily tested for, with more accuracy than the salt test. Muriatic acid and pH testing would probably be the easiest, as the strength of the acid doesn't change with age. But LC would be ok as long as it was a fresh bottle.

--Jeff

 

[duraleigh]

got a pic of that pool?

 

[poolurker5]

Not sure about the pool volume thing. I don’t wait for my salt to dissolve. I dump it in and then use my pool brush to stir it around until it’s completely dissolved. Usually only takes around 10 minutes or so. Then I turn on the pump to its two hour quick clean cycle to mix it and forget about it.

This is what I also do.
For a single 40lb bag, do you still need to turn off the SWG while it mixes, or can it safely stay running for one bag?

 

[Orion7319]

This is what I also do.
For a single 40lb bag, do you still need to turn off the SWG while it mixes, or can it safely stay running for one bag?

For 1 or 2 bags I just let it run usually. I have never noticed it mess it up for 1 or 2 bags. I mean when I get a heavy rain and the water level goes up and inch or 2 I know my salt is more diluted. Over time the salt cell seems to adjust to that, but not right away. Others might say differently and it might depend on your system.

 

[mjmeans]

Yes I realize that. But the meter shows Ccf.

got a pic of that pool?

Yes. Satellite image taken close to 20 years ago at theoretically 1 inch per pixel. It was covered by a solar blanket at the time. I don't have a picture without it.