Pool evaporation

[Katodude]

Hey with a quick search I found this old thread.

Are Pan Evaporation Rates applicable to pools?

After seeing several posts with users wondering how certain chemicals could build up in their water over time (e.g., salt and CH) and considering my on-going plans to eventually install a rainwater collection system from my flat roof gutters, I got to wondering about the applicability of pan...

www.troublefreepool.com

Has anyone played with the spreadsheet?

This is the time of year where I usually have a high degree of evaporation, but now I also think I have a pool leak. I can never get a bucket test to work. But I am losing about 1/2” overnight.

 

[AUSpool]

1/2” overnight seems like a lot. I would be giving that bucket test another go. I don’t recall the spread sheet but ages ago I was given the link to an online equation or calculator that I used for predicting evaporation. I think @JoyfulNoise gave me the link. There is a point where high wind velocity and temps increase the evaporation quite dramatically. For me it was the wind with an exposed pool.

 

[Katodude]

I have tried and tried the bucket test and I am just no good at it. The spreadsheet says I should have a .4” daily drop.

Here is some more data.
The pool reached a high of 80.5 degrees yesterday.
This morning the pool was 76.5 degrees for a drop of 4 degrees.
Air temperature was a low of 63 degrees overnight.

 

[AUSpool]

0.4” is not far from 0.5” but you said it was 0.5” overnight, add in day time loss and I expect your over an inch per day. You really need to factor in wind velocity and humidity.

(It seems a little odd using decimals for the medieval measurement system…)

 

[AUSpool]

I have tried and tried the bucket test and I am just no good at it.

It shouldn’t be that hard. All you need is a bucket, a brick for a weight, and a pool step, second step preferably. The trick is finding the right size bucket so the top of the bucket is only a little above the pool level. Then no splashing, or rain for a day, or two preferably.

 

[Bperry]

I have tried and tried the bucket test and I am just no good at it. The spreadsheet says I should have a .4” daily drop.

Here is some more data.
The pool reached a high of 80.5 degrees yesterday.
This morning the pool was 76.5 degrees for a drop of 4 degrees.
Air temperature was a low of 63 degrees overnight.

A trick to make it easier. Put the bucket (with a brick inside on a step so it’s sticking up out of the water as little as possible. Then add water to the pool until it just overflows into the bucket. Then you know the levels are matched and don’t need to use tape or a sharpie.

 

[Mdragger88]

@Katodude
Do you have a cover? If so perhaps you can deploy it & see if you’re still loosing the same amount.

 

[Katodude]

Lost 3/4” in 24 hours. It’s a leak.

I am calling the leak company.

 

[Mdragger88]

Have you done any line plugging/investigation/isolation?
Got an overflow drain? Autofill? Some can have siphoning issues.

Leak Detection

A number of things can cause leaks in your pool. You can learn tricks for leak detection and how to pinpoint where your pool is losing water.

www.troublefreepool.com

 

[Newdude]

Maybe it's been a long time coming and is finally bad enough to notice. Here's to hoping the magically disappearing CYA does better after.

 

[Katodude]

I am very bad at leak detection. I have read all the stuff, bought the dye, squirted stuff all over the place and can find nothing.

Also the confirmation of a leak is my CH level is dropping, when it should be rising as I add water to the pool.

At this point it’s just easier to pay the $395 for them to spend the 10 minutes it will take to find the leak in my skimmer (it’s always in the skimmer). Appointment is made, they will be out her next Tuesday.

 

[Katodude]

Maybe it's been a long time coming and is finally bad enough to notice. Here's to hoping the magically disappearing CYA does better after.

It’s probably only been leaking for about a month. The tell tale sign for me is CH level and salt level (which reminds me I need to buy new salt reagents and my refills). I test CH with a 25ml sample to get 10ppm precision. Just an extra level of assurance for me since I run my CH low.

So it’s unlikely that my CYA problem is related, but here is hoping. In any case I bought a 50lb bucket of the expensive stuff that I forget who around here said worked better. We will see.

 

[Darin]

Also the confirmation of a leak is my CH level is dropping, when it should be rising as I add water to the pool.

No your fill water is the same hardness as the water leaking. That is unless you are gonna let a bunch like 25% of your pool water leak out then compare.

 

[Darin]

Evaporation testing is a bit tricky when comparing different areas of country.
Variables:
Are you testing on June 21 the longest daylight time of the year solar IR vs. short daylight hours.
Water temp
Wind speed on top of water.
turbulence from returns
Humidity

So when testing your pool make sure to keep the bucket filled very close to pool surface and don't use a dark colored bucket that will absorb solar heat. Sounds like you will get to the bottom, umm bad choice of words, get to the leak soon.

 

[mgtfp]

No your fill water is the same hardness as the water leaking.

As water evaporates, leaving CH behind, and gets replaced with calcium containing fill water, CH accumulates over time.

 

[Darin]

CH accumulates over time.

If doing small refills one would not notice. If tracking year to year yes may possibly notice. Also if on city water, sources may change throughout the year. Very hard to track using hardness.

 

[Katodude]

Actually I think CH is a great way to track a leak. If CH is stable or goes up, that is most likely inconclusive. However, if your fill water has a lower CH than your pool (which it is in my case, and most cases) and you CH is dropping while you are adding water over a span of weeks, that is going to lean heavily towards a leak.

 

[mgtfp]

If doing small refills one would not notice. If tracking year to year yes may possibly notice. Also if on city water, sources may change throughout the year. Very hard to track using hardness.

Unlikely to notice the accumulation from one test to the next, but depending on the hardness of the fill water, the amount of evaporation and rain, and backwashing frequency, it will be noticeable over the course of a season. There are many cases here where CH accumulated rather quickly.

In my case dilution from draining rain excess (after the rain has mixed in) in winter dominates over CH being added by fill water additions in summer. I see a small over summer, but a larger drip over winter, so I raise CH from time to time with calcium chloride.

I wanted to point out that fill water CH is very unlikely to be the same as the fill water CH, unless after a fresh fill.

 

[Katodude]

So leak guys were here and could not find a leak. UGH.

So they put in a bucket for a bucket test and asked me to send them pictures tomorrow.

 

[AUSpool]

The leak guys did that. I would have put it next step down, probably even the next one. There will be a variation in temperature and air velocity. Maybe they know how to account for it? I guess they pressurized the plumbing and found no leaks there but the bucket suggests they are still unsure about the shell?