Strange Salt Level Readings

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RobbieH

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TFP Expert
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Aug 30, 2010
4,038
Dallas, TX
All I can think of! Strange.

As you know, I recently finished my SWG install. I have an estimated 44,000 gallon pool based on measurements and based on how the pool reacts to chemical additions.

I added thirty 40 lb bags to the pool. A day later (pump running 24/7) the SWG says low salt, below 2500 ppm, AquaChek test strip reads 6.2 - 2830 ppm.

I added 5 more bags of salt this morning (200 lbs), SWG now says 2800 (getting there), test strip reads the same 6.2 - 2830 ppm. Pump still running non-stop. Also, I ran my robot last night and early this morning for a total of 6 hours, test came out the same before adding the salt as it did last night.

Pool temp is 55, but even letting the test sample sit in the house to warm up hasn't affected the results.

Today and yesterday are the first time I've tested for salt. Am I doing something wrong? Although I have more salt on hand, I'm reluctant to add it until I know the test results are accurate.
 
Re: Strange

1,400 pounds of salt added to 44,000 gallons will raise the salt by 3,800 ppm, and that's in addition to whatever salt level you already had in the fill water. I recommend that you test it with the K-1766 Taylor Salt Test, or a freshly calibrated meter.

Also, you should test the fill water for salt to know what level you are starting from.
 
Re: Strange

I'd hold off. Could be cold water temp throwing things off. Have you turned on the SWCG yet? That will also give you a measurement but i would take it with a grain of salt. I believe the reading could be as far as 400 off.
 
Re: Strange

Unfortunately I don't have the K-1766. There's a commercial supply near me so I tried to get one there. When they said they were out, I forgot to order one from TFTestkits.net (I do buy a lot there). I still want to get one on the way... But, several folks told me the AquaChek strips are also accurate.

Fill water? I haven't had to fill in a long time. We have had lots of rain. Essentially at this point I just want it in balance, so I'm taking my time.

Pool Calculator says 1289 lbs. And yes, I should have already had salts in the pool, that's why without the test kit I've been going slowly. But either way, if these strips are accurate, why would it read exactly the same after adding another 200 lbs?

All the new salt has been dissolved for hours, about to go start the robot again to assist the pump.

EDIT:
Yes, I have turned on the SWCG long enough to get a reading, see above, it's showing higher salt after adding the additional 200 lbs, but the strips are not. And note I let the test water warm up before testing with strips.
 
Re: Strange

What's your pump run time? And what % setting are you using on the SWCG. If you're not getting a low salt indicator I'd save the salt till you get your K-1766. It's easier to add more than overshooting. LOL
Have you checked your TC/FC levels? Are they starting to rise yet.
 
Re: Strange

My FC was already high (8) so I haven't run the SWCG for longer than it takes to test the water. Pump has been running non-stop. I like the idea of waiting, I will order the 1766 now.

FC was high because I ran the Liquidator wide open to clear the bleach out before draining.
 
Re: Strange

To get all the salt distributed, and to get the water clear from not having a pump for several days. I shut it off last night, but running it again today. My main concern has been making sure the salt is distributed throughout the water to make sure I get accurate readings.

Just went out and checked the equip, SWCG reporting low salt again, strip test shows 2610. The K-1766 is on the way. Chlorine is still way high, so no need to run SWCG right now. Not going to add salt or run the SWCG until I know I need it, and know my tests are accurate. Water is SPARKLING clear today, so going to put pump back on 2 hour cycle.
 
Re: Strange

If your water is 55 degrees, it's too cold fo ryour SWCG to operate. It doesnt matter what the strips say your salt is, or what the Taylor test says your salt is. All that matters is what your SWCG thinks the salt is. At 55 degrees, the sensor is not accurate. As I've posted before, these things dont actually read salt; they read water conductivity. Conductivity of the water is dependent on dissolved salts, and temperature. I wish the manuals on the SWCG would actually tell you that once water goes below 70 degrees, the ability of these things to read the salt is diminished. Once the water goes below 66-63, forget getting an accurate reading. You are running yourself crazy over this when all that wrong is the waters to darn cold.
FWIW, I've never had any luck with strips. You say the SWCG is reporting around 400 ppm difference than the strips. Thats within the range of the error on both methods. Please stop worring about it. Once the water gets back in to the low 70's, everything should go back to normal. And, cold water doesnt dissolve salt very well either. Chorinate with bleach over the winter.
 

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Re: Strange

Surprisingly when I did the inital 30 bags, I expected the salt to take 2 days to dissolve. It was gone overnight. The next 5 bags were gone in 2 hours.

It's possible my pool size estimate is off, but I'll hold until water temps get up, and I'll test with the Taylor kit at room temp just for the fun of it.
 
Re: Strange

bk406 said:
I wish the manuals on the SWCG would actually tell you that once water goes below 70 degrees, the ability of these things to read the salt is diminished.
Click to expand...
I have heard that Pentair SWGs have this problem but the ability of any SWG to show the correct salt level should not be diminished due to just water temperature. It just depends on how well the unit is calibrated. My Goldline SWG will report the correct salt level all the way down to 50 degrees where it then shuts off due to temperature. I think the problem is that not all manufactures properly calibrate the SWG for the entire operating temperature range as they should. But I have not heard if CompuPool SWGs have this same problem.

Also for me, the test strips tend to read about 500 ppm too high but the drop kit seems to match my SWG display within a 100 ppm and at all water temperatures above 50F.
 
Re: Strange

First, there are two types of temperature compensation in SWGs. One is for the chlorine production, which my unit does not have and the other is just for the salt read out which my unit has. I know for a fact that my Goldline has temperature compensation because 1, it reads the same salt level from 50F up to spa temps at 105F. I have tested this on my own spa in about an hours time. If it didn't have a temperature calibration, it wouldn't be able to do that and the salt level would vary with temperature. And 2, I confirmed this directly with a Goldline engineer. It is true that not all SWGs do this and I believe that the Pentair unit is one that does not but the Goldline AquaLogic most certainly does temperature compensation for the salt read out.
 
Re: Strange

I took a quick read through the CompuPool CPCS48 manual and it doesn't indicate that there is a minimum operating temperature where it shuts the unit off so it sounds like it is producing chlorine. Unless it alarms for any reason, I would leave it alone for a week and then see what the salt level reads. I have found it can take several days for salt levels to stabilize after adding salt. BTW, what is your water temperature?
 
Re: Strange

Water temp according to the CPSC is 55. My thermometer that floats in the pool somehow strangely disappeared. FC is still high, so I'm not running the SWCG at all, other than bringing it up long enough to see what it thinks salt and water temp levels are.
 

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