Opening pool..Determining how much Salt

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C

Cahnman

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Mar 10, 2017
11
Marietta
So last year I paid some jack wagon to maintain my pool. This year I'm saving some money....with your help of course!! I opened up cover last week and it was a bit green. Got the leafs that found their way in out of the pool. Got a handle on PH, FC, etc. The water is crystal clear now. I cleaned the DE grids per a thread here. Got it vacuumed. I've learned so much already. I just am not sure about the whole SWG. I ordered the TF-100. My pool guy last year gave me some strips. I already learned about how you feel about "guess strips". I haven't turned on my SWG yet this year. How do I know how much Salt to add if any? Does the TD-100 test this? Any good threads or links on this subject. Thanks for the help!

Kevin
 
My preference is to use the K-1766 salt test kit. Strips can work, but I have never found them to be more accurate than +/-400ppm and they can easily go bad and give spurious readings if the conditions are not right. Because you live in a place where rain dilution can be an issue, you will likely test for salt more than I do (I only test once or twice per season) so having a high quality test kit is key. The salt test also measures chloride ion (Cl-) directly and so it is an exact test for salt concentration as opposed to any other method which must use a proxy to determine salt. In the case of strips, it's usually the capillarity of the solution. The test chemicals in the K-1766 have no interferences and they will last a long time if the kit is stored in a cool, dry place.
 
Cahnman said:
I just am not sure about the whole SWG. I ordered the TF-100. My pool guy last year gave me some strips. I already learned about how you feel about "guess strips". I haven't turned on my SWG yet this year. How do I know how much Salt to add if any? Does the TD-100 test this? Any good threads or links on this subject. Thanks for the help!

Kevin
Click to expand...
Your signature shows you have Hayward AquaRite SWG. The SWG system itself will measure and report what your salt level is (you have same system I do). Once you start up your SWG take the reading then use the Pool Math calculator. Enter your pool size (gallons) what your SWG system reports as the "Now", for "Target" I would recommend 3200 (acceptable range per Hayward is 2700-3400). The calculator will calculate how much salt (if any) you need to add to your pool. If it's within the 2700-3400 you may wish to nothing for now, though ideally I'd set the minimum level at 3000.

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JoyfulNoise said:
My preference is to use the K-1766 salt test kit. Strips can work, but I have never found them to be more accurate than +/-400ppm and they can easily go bad and give spurious readings if the conditions are not right. Because you live in a place where rain dilution can be an issue, you will likely test for salt more than I do (I only test once or twice per season) so having a high quality test kit is key. The salt test also measures chloride ion (Cl-) directly and so it is an exact test for salt concentration as opposed to any other method which must use a proxy to determine salt. In the case of strips, it's usually the capillarity of the solution. The test chemicals in the K-1766 have no interferences and they will last a long time if the kit is stored in a cool, dry place.
Click to expand...
I agree that the test strips are using but since the AquaRite will measure the salt level in pool, why have a separate test kit?
 
The test kit is nice to verify that the SWG is working properly. If the salt readings are way off from the box, it can alert you to a potential problem. Highly recommended.
 
bobandsherry said:
I agree that the test strips are using but since the AquaRite will measure the salt level in pool, why have a separate test kit?
Click to expand...

The Hayward AquaRite has a good internal algorithm for reporting salinity level that is close to real-world, but it, in and of itself, is still a proxy method of measuring salinity. All SWG's that report salinity are actually reporting TDS and, to be even more specific, they are reporting the electrical conductivity (EC) of the water passing through the cell. So, the basic algorithm is this -

1. Measure voltage, current and temperature
2. Calculate the conductivity of the water in the cell
3. Use a series of correction and scaling factors to output salinity based on factory calibrated models.

Haywards do that algorithm well, Pentair's not so well and I have no feel for Jandy. In the above method, there are interferences. Chloride (Cl-) is only one of several ions in solution that can conduct electricity. Solution conductivity is also affected by pH and temperature. So there's lots of "other factors" that can vary and cause the conductivity to change which have nothing to do with actual salt levels. Also, once a salt cell starts to build up scale on the plates or if the coating becomes damaged, the reported salinity levels will be far off from the actual value. In fact, that is one way to diagnose the health of an SWG - if the reported salinity levels fall but the actual levels remain the same, you either have scale on the plates or a damaged coating.

On the contrary, the K-1766 is a chemical test for chloride ion based on Mohr's Method (also known as the argentometric method). It is a titration of chloride ions, and only chloride ions, using silver nitrate. The reaction is mostly independent of pH in the range of pH one finds a pool to be in and is not interfered with by any other ion in solution (unless you happen to have bromide ions in solution or cyanide anions). So the K-1766 measures the exact salt level and reports that with an tolerance that's based on the test volume. So, the standard test uses a 10mL water sample and gives +/-200ppm. However, all you need to do is use a 25mL water sample and the tolerance becomes +/- 80ppm. A 50mL water sample will have a tolerance of +/- 40ppm. That is both exact (measures chloride only) AND more accurate than any other method available.
 
Give at least a few hours of circulation before testing chemistry. If you need to add salt, turn off the SWG for at least 12 hours to allow for good mixing.

Brushing, running a cleaner and/or using the main drain will speed up mixing.
 
Cahnman said:
Really appreciate all the feed back. So....should I Run my SWG for a few days before I run the "salt water test" or does it not matter? I guess running SWG just creates FC.
Click to expand...
You don't need days. Before you start up your SWG inspect your cell and clean it if necessary. To JoyfulNoise's comment above, you don't want scale on your cell plates as it can affect the Hayward salt level reading at your Hayward box.

Once cell is clean, set the output to 50% and run for an hour. Then check the salt level reading at the Hayward box.

When you first start up the SWG you should probably also reset the salt reading by doing an update to get an Instant Salinity reading. To do this (from the manual):


  1. Slide the Main Switch to the "Auto" position.
  2. Push the Diagnostic button repeatedly until "-xxxx ppm" appears on the display.
  3. Slide the Main Switch from "Auto" to "Super Chlorinate" and back to "Auto".
  4. Push the Diagnostic button to exit.

This will clear the Salt level reading (which could be held over from last year) to the Instant Salinity reading and then begin to correct the reading based on the running averages. You'll want to do this after you add salt as well.

While SWG is running you can check the indicators to see if the "check salt" or "inspect cell" lights are lit. "Check Salt" would indicate that salt level is too low. "Inspect cell" flashing would indicate that cell efficiency is reduced (or that cleaning wasn't properly done), if it steady lit then SWG is not producing chlorine. But refer to manual for more information on the indicator lights.

Lastly, before you turn on your SWG you may want to use your salt strips to ensure there is salt in the water as you don't want to run SWG with no salt. This is just a precaution as there should be salt since you were running it last year.

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Thanks JoyfulNoise for the indepth response on the Hayward SWG reading. I've found mine to be pretty much spot on, but mine is less than a year old and I keep the plates clean. But can see if someone has not properly maintained their cell or it's past it's prime how the reading could be deceptively wrong.
 

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I would add one thing
Salt is pretty cheap if you buy the stuff thats NOT for pools. Go to the section of the store that sells pure salt for water softners etc
and if pool math says you need 6 40 lb bags add 5, let things circulate and recheck - its REALLY easy to add more and it dissolves QUICK
 
JoyfulNoise said:
The Hayward AquaRite has a good internal algorithm for reporting salinity level that is close to real-world, but it, in and of itself, is still a proxy method of measuring salinity.

On the contrary, the K-1766 is a chemical test for chloride ion based on Mohr's Method (also known as the argentometric method). It is a titration of chloride ions, and only chloride ions, using silver nitrate. The reaction is mostly independent of pH in the range of pH one finds a pool to be in and is not interfered with by any other ion in solution (unless you happen to have bromide ions in solution or cyanide anions). So the K-1766 measures the exact salt level and reports that with an tolerance that's based on the test volume. So, the standard test uses a 10mL water sample and gives +/-200ppm. However, all you need to do is use a 25mL water sample and the tolerance becomes +/- 80ppm. A 50mL water sample will have a tolerance of +/- 40ppm. That is both exact (measures chloride only) AND more accurate than any other method available.
Click to expand...

I went and purchased the K-1766 and did my first test. Using 10ml the kit showed 3000, my pool cell is reporting 3200 so within tolerance levels of each other. I was going to test with 25ml but no instructions on how many drops of R-0630 to use. Mathematically it should be 2.5 drops but how can you get half a drop :) Do you use 2 or 3 drops? And then what are you using as the measure for each drop of R-0718?
 
bobandsherry said:
I went and purchased the K-1766 and did my first test. Using 10ml the kit showed 3000, my pool cell is reporting 3200 so within tolerance levels of each other. I was going to test with 25ml but no instructions on how many drops of R-0630 to use. Mathematically it should be 2.5 drops but how can you get half a drop :) Do you use 2 or 3 drops? And then what are you using as the measure for each drop of R-0718?
Click to expand...

You don't have to scale up R-0630 as it is the indicator (potassium chromate) for the test. Because silver chromate is a brick red color, it's very easy to distinguish it when the last of the chloride is titrated away by the silver nitrate. Once all of the chloride reacts with the silver ions being added to the solution, the silver is left to react with the chromate. You can use an extra drop of the indicator if you want, all it will do is make the brick red color more intense.

As for the titrant (R-0718), it's just simple scaling - if 10mL sample size gives 200ppm/drop, the a 25ml sample size give (10/25) * 200 = 80ppm/drop. Given your water is around 3000ppm, you might want to use a 20mL water sample which will give you 100ppm/drop as that is more than enough precision for your needs. I would only use a 25mL or 50mL water sample if I were testing tap water as my municipal water is ~160ppm sodium chloride.
 
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