Underground Leak or Evaporation?

[Kit]

Earlier in the summer I posted a concern of a possible leak in my in-ground spa. The "bucket test", however, suggested that no leak was obvious.

Over a 40-day period, I kept a log of the water level in the spa with the auto fill OFF & the cover in place except for about 1 hour daily. The total decrease in the water level was 2". There was no splash out during that period (not even into the auto cover vault).

Therefore, as a result of the bucket test & no evidence of splash out, I can only assume that the decrease in the water level was due solely to evaporation. Am I thinking correctly here? If so, does this amount of water loss due to evaporation seem excessive for a covered 2,500- gallon spa measuring 10' X 14'?

For the past 22 days, the auto fill has been ON. The salt level has fallen from 3,000 ppm to 2,450 ppm (using the Taylor drop test). Does this seem to be consistent with the above assumed evaporation loss?

Do keep in mind that during this 40-day test period, the air temperature has been between 80℉ & 100℉.

As usual, thank you so much for your help & expertise.

Kit

 

[ping]

There could be a very slow leak, but it is hard to say with your test results. If the salt level continues to lower then I would say there is a good chance that it is a leak. But right now, the salt test is too close to the margins of error in the test itself.

For now I would keep track of the salt level and see if it continuously drops.

 

[Kit]

I appreciate your comments. I guess that is where I am at on this issue: is there a slow leak or is it simply normal evaporation that is triggering the auto fill and, thus, lowering the salt level.

 

[mas985]

or is it simply normal evaporation that is triggering the auto fill and, thus, lowering the salt level.

That would not lower the salt level. If there is only evaporation, the salt should remain the same.

Some additional questions:

While in use with the cover off, how warm is the water and how cool is the air?

 

[Kit]

I guess I am a bit confused. Although evaporation itself will not lower the salt level, as the water level falls, this will trigger the auto fill. It is the inflow of fresh water from the auto fill that will lower the salt level. Am I correct?

When the spa is in use, the water has been about 92F & the air temperature about 85 - 92F.

 

[mas985]

It is the inflow of fresh water from the auto fill that will lower the salt level. Am I correct?

No. Water evaporated too so there is no net change in water and no net change in salt, therefore no change in salt ppm. The autofill keeps the water at the same level all the time.

Evaporation should be about 0.02" per hour. Over 22 hours (days), that would be about a 1/2".

 

[Kit]

No. Water evaporated too so there is no net change in water and no net change in salt, therefore no change in salt ppm. The autofill keeps the water at the same level all the time.

Evaporation should be about 0.02" per hour. Over 22 hours (days), that would be about a 1/2".

Mark,

Ah, I finally get it. Water evaporates; not salt. Thus, the fresh water from the auto fill is merely replacing the water lost due to evaporation. Thus, salt ppm should remain constant.

So, a decrease in the salt ppm can only be due to either (1) a leak or (2) splash out. Do I have it right?? Thank you.

Kit

 

[mas985]

Yes, lower salt levels are due to either leaks or splash out. You must actually remove the salt.

For a 2500 gal spa, the removal of 550 ppm of salt is 18% of the water+salt or 458 gallons of water+salt. Over 22 days, this is 21 gallons per day.

Besides the plumbing, with plaster/gunite, common spots for leaks is where plastic meets the plaster such as the skimmer. Or you could hire a leak detection company.

 

[ping]

2" of water is only 190 gallons in his pool. I say give it more time and keep testing the salt level.

 

[Kit]

2" of water is only 190 gallons in his pool. I say give it more time and keep testing the salt level.

Yes, I will continue to test the salt level without adding any additional salt. However, it seems to me that if the salt level continues to fall, there is undoubtedly a leak somewhere (since I have ruled out any appreciable splash out). In the meantime, I have a call into the spa builder to pressure test the plumbing.

 

[Kit]

Pressure Testing Advice

I have a suspicion that I might have a small underground leak in my in-ground spa. During the past 40 days, the water level fell a total of 2" with a half hour of use daily & the auto cover in place the remainder of the time. I have been told that this is quite normal for my spa (see size below) with temperatures in the 80F - 100F range. In addition, I did the "bucket test" as recommended on this forum. There was no appreciable difference in the water level in the spa & in the bucket.

However, the salt level fell over a 3 week period from 3350ppm to 2600ppm. I then added salt to raise the level back up to 3200ppm. During the following 30-day period, the salt level fell from 3200ppm to 2150ppm. I took these readings from both the IntelliChlor SWG readout & the Taylor reagent test kit.

Since I confirmed that there is no appreciable splash out whatsoever, I am assuming that the falling salt level must be the result of a leak. (Water lost through evaporation & then replaced by the auto fill should not affect the salt level, right?).

Here is where I could use some expert advice since the folks on this forum have been extremely helpful in the past. The spa builder will be pressurizing the spa for a 24-hour period. If the test results show no pressure loss, can I safely assume that there is no leak in the underground plumbing? What other locations might be checked for leaks? If all of these diagnostics indicate no leaks whatsoever, can there be any other explanation for the fall in the salt level?

Thank you so much for your patience with a new spa owner & for your expertise. It is truly appreciated!!

Kit

 

[Kit]

Re: Pressure Testing Advice

Here is where I could use some expert advice since the folks on this forum have been extremely helpful in the past. The spa builder will be pressurizing the spa for a 24-hour period. If the test results show no pressure loss, can I safely assume that there is no leak in the underground plumbing? What other locations might be checked for leaks? If all of these diagnostics indicate no leaks whatsoever, can there be any other explanation for the fall in the salt level?

Thank you so much for your patience with a new spa owner & for your expertise. It is truly appreciated!!
Kit

The spa has been pressurized for the past 6 hours & the pressure is holding at the benchmark level of 10 psi. If the pressure holds for the remainder of the test period, I am perplexed as to why the salt level has been falling (see my post directly above). Splash out has been essentially zero. I would appreciate your thoughts prior to talking with the spa builder tomorrow.

Thank you.

Kit

 

[kellyfair]

I'm not sure how accurate the test is. I can go from 3000 one day to 2600 the next day back to 3100 the day after that, all without adding salt, water or anything else.

 

[mas985]

With a gunite spa/pool, there are other areas that can leak that cannot be pressure tested but can be dye tested. These are areas where the gunite meets plastic like near returns, skimmers and main drains.

 

[Kit]

I'm not sure how accurate the test is. I can go from 3000 one day to 2600 the next day back to 3100 the day after that, all without adding salt, water or anything else.

Kelly: Indeed, I have noticed the same with both the readout from the SWG & the Taylor reagent test kit. In fact, I have seen daily swings of up to 1,000ppm. In spite of this, there seems to be a downward trend in the salt level. Most perplexing.

If anyone might have any other thoughts, I would surely appreciate it. Thank you.

Kit

 

[Kit]

With a gunite spa/pool, there are other areas that can leak that cannot be pressure tested but can be dye tested. These are areas where the gunite meets plastic like near returns, skimmers and main drains.

Good point. However, with the auto fill off, I did the "bucket test" which indicated no leak.

So here is where I am at:

1. With the spa pressurized at 10 psi for 48 hours, the pressure held constant.
2. There is virtually no splash out.
3. With the auto fill off, the bucket test indicated no leaks.
4. With the auto fill off & auto cover in place (except for about 1 hour daily), water level fell about 1/16" daily at the most. This seems likely the result of evaporation since air temperature was 85F - 100F.

So with the likelihood of no leaks nor splash out, why is the salt level falling?

 

[mas985]

Good point. However, with the auto fill off, I did the "bucket test" which indicated no leak.

Then why did you bother with the pressure test?

The leak around the skimmer or MD or returns could be very slow and difficult to see with a bucket test. The fact is if you are seeing salt levels decreasing, you are losing water other than evaporation. There is no other explanation.

However, your testing seemed to be a bit flawed given the drop in water because the drop is salt did not match the drop in water level.

 

[Kit]

Then why did you bother with the pressure test?

The leak around the skimmer or MD or returns could be very slow and difficult to see with a bucket test. The fact is if you are seeing salt levels decreasing, you are losing water other than evaporation. There is no other explanation.

However, your testing seemed to be a bit flawed given the drop in water because the drop is salt did not match the drop in water level.

Mark: You are correct about the redundancy of the pressure test. Since the spa is new & under warranty, I wanted to be absolutely positive about the results of the bucket test. Maybe it was for my peace of mind.

Forgive my ignorance, but could you please clarify your statement that "However, your testing seemed to be a bit flawed given the drop in water because the drop is salt did not match the drop in water level". Thank you.

 

[mas985]

During the past 40 days, the water level fell a total of 2" with a half hour of use daily & the auto cover in place the remainder of the time.

Your spa is 154 sq-ft and 2" is 192 gallons or about 4.8 gallons lost per day.

During the following 30-day period, the salt level fell from 3200ppm to 2150ppm.

Your spa is 2500 gallons and you said the salt level drop by about 1000 ppm over 30 days. In order to get 1000 ppm drop in salt level, you would have to have lost about 1/3 of the water which is 833 gallons or 27.8 gallons lost per day.

So a huge difference between the two. One of the two measurements is not correct.

 

[Kit]

Thank you, Mark, for the explanation. In fact, one of the possibilities I am looking into is the accuracy of the readout on the EasyTouch control panel. I spoke with one of the techs at PentAir & advised him that at times the readout indicated daily fluctuations of 600 - 1000 ppm. He felt that was unusual & will likely issue a warranty work order to check into the matter. (Interestingly, the Taylor reagent drop test also showed several daily fluctuations in the 400- 600 ppm range. Is this normal?).

So, I will explore the possibility of a dye test around the fittings, drains & skimmer. Along with the previously-done pressure test, this should rule out a leak issue.

Let me take the time to thank you for your help. As a new spa owner, I truly appreciate your patience & the expertise of someone like yourself.