Underground Leak or Evaporation?

[mas985]

(Interestingly, the Taylor reagent drop test also showed several daily fluctuations in the 400- 600 ppm range. Is this normal?).

Each drop is 200 ppm and it is pretty easy to miss the color and add 1 too much or 1 too little so between two tests, it wouldn't be too difficult to be off by 2 drops (1 test high and 1 test low). It is important to try and be consistent with the test so you might want to take a picture of the first test and use that as a reference for the next test.

Also, you really can't use the SWG readout for absolute salt levels especially for Pentair because their cell calibration seems to be very sensitive to water temperature so it often gives inaccurate salt levels.

 

[Kit]

Each drop is 200 ppm and it is pretty easy to miss the color and add 1 too much or 1 too little so between two tests, it wouldn't be too difficult to be off by 2 drops (1 test high and 1 test low). It is important to try and be consistent with the test so you might want to take a picture of the first test and use that as a reference for the next test.

Also, you really can't use the SWG readout for absolute salt levels especially for Pentair because their cell calibration seems to be very sensitive to water temperature so it often gives inaccurate salt levels.

Good point. I count the last drop that turns the solution from a milky cream color to a dull, reddish brown.

I have heard that comment regarding the SWG readout on this forum. That might explain why I might have been unnecessarily adding salt.

Thank you.

 

[Kit]

Just a follow-up on my last post. Having likely ruled out the possibility of a leak (as a result of the bucket test & pressure test), my spa builder said that adding 10 lbs. of salt maybe every 5-6 months was normal. Is there any validity to this statement? And if so, why?

Also, in my above post, could someone please address my concern for the fluctuations in the salt level readings in both the IntelliChlor & Taylor kit readouts?

I would truly appreciate it. Thank you so much.

Kit

 

[mas985]

I think we covered both of these already but to summarize:

Loss of salt is only by splash out, overflow or a leak

Fluctuations of salt levels in the Intellichlor come from either water temperature change, dirty cell, failing cell or actual salt level changes.

Fluctuations in Taylor test kit are only due to operator error or actual salt level changes. As far as know there are no interference's to this test.

 

[Kit]

Sorry for being redundant, Mark. Since I am getting conflicting information from various sources, I'm having difficulty sorting out my problem. Not personally having expertise in this area, I sometimes feel like I am being batted back & forth like a ping-pong ball.

 

[mas985]

What is the conflicting information and source of the information?

 

[JoyfulNoise]

The K-1766 has an accuracy only limited by the water sample volume. The standard test calls for a 10mL water sample which gives a resolution of 200ppm/drop of titrant.

If you use a 40mL water sample you will get a +/-50ppm/drop resolution.

The K-1766 measures chloride ions (Cl-) only. The only other interferences are from bromine, iodine and cyanide...none of those would be in your spa.

 

[Kit]

What is the conflicting information and source of the information?

In spite of the bucket test, 2 pressure tests & a 30-day monitoring of the water level, my spa builder insists that adding approximately 10 lbs. of salt to a 2,500-gallon spa every 5-6 months in normal. I am hard-pressed to understand his reasoning. (BTW, I am awaiting his follow-up response). I might add that the 30-day monitoring period I am referring to showed that I was losing about 1/32" of water each day. I assumed this could be accounted for by evaporation in 85F - 100F temps even with the auto cover in place.

Your point that the salt level readout from the IntelliChlor will vary with water temp seems to be validated by my own recorded data. On the other hand, one of the techs at PentAir says that a daily fluctuation of 600 - 1000 ppm is excessive.

- - - Updated - - -

The K-1766 has an accuracy only limited by the water sample volume. The standard test calls for a 10mL water sample which gives a resolution of 200ppm/drop of titrant.

If you use a 40mL water sample you will get a +/-50ppm/drop resolution.

The K-1766 measures chloride ions (Cl-) only. The only other interferences are from bromine, iodine and cyanide...none of those would be in your spa.

Matt: I have been using a 10 ml water sample & noted daily fluctuations of up to 400 - 600 ppm.

 

[JoyfulNoise]

If you truly want to track salt concentration as a proxy for leak detection, then your testing needs to be more calibrated (i.e., use a larger water sample to gain a deeper titrant precision) and you need to ignore the IC salinity output. The Pentair ICs are probably the worst of the breed when it comes to measuring salinity and I all but ignore the readout value and simply look for the system to say that the salt cell is OK.

Track your salinity every few days with the K-1766 and turn off your autofill. Add fill water manually and use a hose-end water meter to get precise input volumes. You'll also want to measure the salinity of your fill water as all municipal supplies have some residual chloride level (mine fill water has ~160ppm chloride in it).

 

[JoyfulNoise]

Matt: I have been using a 10 ml water sample & noted daily fluctuations of up to 400 - 600 ppm.

Yes, that can happen. Unless you are using a SampleSizer to measure your water volumes (or some other accurate method), your 10mL sample size can be off a bit and add to the error in the test. This is why a larger sample size is a little better - being slightly off in viewing the meniscus matters less.

 

[pooldv]

Yes, +1 on the IC-40 salinity reading not being accurate and very temperature dependent. My cell gave me a low salt warning last week when the water temp dropped to 79-80. Temp has been 81 to 86 this week and the salt level is green again. This is 100% temp related, no rain, no change in salt level, etc.

 

[Kit]

If you truly want to track salt concentration as a proxy for leak detection, then your testing needs to be more calibrated (i.e., use a larger water sample to gain a deeper titrant precision) and you need to ignore the IC salinity output. The Pentair ICs are probably the worst of the breed when it comes to measuring salinity and I all but ignore the readout value and simply look for the system to say that the salt cell is OK.

Track your salinity every few days with the K-1766 and turn off your autofill. Add fill water manually and use a hose-end water meter to get precise input volumes. You'll also want to measure the salinity of your fill water as all municipal supplies have some residual chloride level (mine fill water has ~160ppm chloride in it).

Matt,

Thank you for your response. I plan to refill my spa in a day or two. Once I get the salt level & my water chemistry back in balance, I will follow your suggestion & test 40ml of water with the K-1766 every few days (rather than the 10 ml I tested in the past). I will ignore the IC readout.

Here are a few additional pieces of the puzzle that might be useful:
1. For 30 days in July, I turned the auto fill off & used the K-1766 to test the water daily. I added no water manually. The daily test results remained in the 2,600 - 3,200 ppm range. During the same period, the water level fell 1/32" daily.

2. I then manually refilled the spa. If my calculations are correct, I added about 136 gallons of fresh water. For the next 15 days, the salt level remained in the 2,800 - 3,000 ppm range with the auto fill still off.

3. Finally, I turned the auto fill back on. For the next 18 days, the K-1766 indicted that the salt level fell from 2,400 to 1,800 ppm.

So, Matt, does this information trigger any particular thoughts regarding any leaks, evaporation or testing anomalies? Thank you so much!

 

[JoyfulNoise]

Does your spa have an overflow pipe to drain off excess rainwater or water build up from precipitation?

 

[Kit]

Does your spa have an overflow pipe to drain off excess rainwater or water build up from precipitation?

No. The auto cover seals off the spa quite well, in addition to the perimeter coping which slopes away from the spa. Keep in mind that we have had virtually no rain during the past 3 months.

If the water level were to rise above 2 - 3" (I would guess), the excess would spill over into the cover vault & exit through a drain.